diff --git a/ApplicationLibCode/FileInterface/RifOpmFlowDeckFile.cpp b/ApplicationLibCode/FileInterface/RifOpmFlowDeckFile.cpp
index 6d4764996f..b7467f2bd1 100644
--- a/ApplicationLibCode/FileInterface/RifOpmFlowDeckFile.cpp
+++ b/ApplicationLibCode/FileInterface/RifOpmFlowDeckFile.cpp
@@ -1061,7 +1061,7 @@ bool RifOpmFlowDeckFile::stopAtTimeStep( int timeStep )
 //--------------------------------------------------------------------------------------------------
 ///
 //--------------------------------------------------------------------------------------------------
-bool RifOpmFlowDeckFile::replaceKeywordData( const std::string& keyword, const std::vector<double>& data )
+bool RifOpmFlowDeckFile::replaceKeyword( const std::string& keyword, const std::vector<double>& data, bool dataKeyword )
 {
     try
     {
@@ -1073,10 +1073,13 @@ bool RifOpmFlowDeckFile::replaceKeywordData( const std::string& keyword, const s
 
         // Get the existing keyword to preserve location
         const auto& existingKw = m_fileDeck->operator[]( keywordIdx.value() );
+        if ( dataKeyword != existingKw.isDataKeyword() )
+        {
+            return false; // Mismatch in data keyword flag
+        }
 
-        // Create a new keyword with the same name and location
-        Opm::DeckKeyword newKw( existingKw.location(), keyword );
-        newKw.setDataKeyword( true );
+        // Create a new keyword with the same settings
+        Opm::DeckKeyword newKw = existingKw.emptyStructuralCopy();
 
         // Keywords ending with "NUM" should be integers (e.g., SATNUM, PVTNUM, EQLNUM)
         bool isIntType = keyword.size() >= 3 && keyword.substr( keyword.size() - 3 ) == "NUM";
@@ -1123,7 +1126,7 @@ bool RifOpmFlowDeckFile::replaceKeywordData( const std::string& keyword, const s
 //--------------------------------------------------------------------------------------------------
 ///
 //--------------------------------------------------------------------------------------------------
-bool RifOpmFlowDeckFile::replaceKeywordData( const std::string& keyword, const std::vector<int>& data )
+bool RifOpmFlowDeckFile::replaceKeyword( const std::string& keyword, const std::vector<int>& data, bool dataKeyword )
 {
     try
     {
@@ -1135,10 +1138,13 @@ bool RifOpmFlowDeckFile::replaceKeywordData( const std::string& keyword, const s
 
         // Get the existing keyword to preserve location
         const auto& existingKw = m_fileDeck->operator[]( keywordIdx.value() );
+        if ( dataKeyword != existingKw.isDataKeyword() )
+        {
+            return false; // Mismatch in data keyword flag
+        }
 
-        // Create a new keyword with the same name and location
-        Opm::DeckKeyword newKw( existingKw.location(), keyword );
-        newKw.setDataKeyword( true );
+        // Create a new keyword with the same settings
+        Opm::DeckKeyword newKw = existingKw.emptyStructuralCopy();
 
         // Create a record with the new data
         Opm::DeckRecord record;
diff --git a/ApplicationLibCode/FileInterface/RifOpmFlowDeckFile.h b/ApplicationLibCode/FileInterface/RifOpmFlowDeckFile.h
index 3e238cecdf..287cd93145 100644
--- a/ApplicationLibCode/FileInterface/RifOpmFlowDeckFile.h
+++ b/ApplicationLibCode/FileInterface/RifOpmFlowDeckFile.h
@@ -90,10 +90,10 @@ public:
 
     bool addKeyword( const std::string& section, const Opm::DeckKeyword& keyword );
 
-    bool replaceKeywordData( const std::string& keyword, const std::vector<double>& data );
-    bool replaceKeywordData( const std::string& keyword, const std::vector<int>& data );
-
     bool replaceKeyword( const std::string& section, const Opm::DeckKeyword& keyword );
+    bool replaceKeyword( const std::string& keyword, const std::vector<double>& data, bool dataKeyword = false );
+    bool replaceKeyword( const std::string& keyword, const std::vector<int>& data, bool dataKeyword = false );
+
     bool replaceAllKeywords( const std::string& keywordName, const std::vector<Opm::DeckKeyword>& keywords );
     bool replaceKeywordAtIndex( const Opm::FileDeck::Index& index, const Opm::DeckKeyword& keyword );
 
diff --git a/ApplicationLibCode/ReservoirDataModel/SimulationFile/RigSimulationInputTool.cpp b/ApplicationLibCode/ReservoirDataModel/SimulationFile/RigSimulationInputTool.cpp
index 1a7f568fda..b53f2c7e52 100644
--- a/ApplicationLibCode/ReservoirDataModel/SimulationFile/RigSimulationInputTool.cpp
+++ b/ApplicationLibCode/ReservoirDataModel/SimulationFile/RigSimulationInputTool.cpp
@@ -195,7 +195,7 @@ std::expected<void, QString> RigSimulationInputTool::updateCornerPointGridInDeck
                                 static_cast<int>( gridAdapter.cellCountJ() ),
                                 static_cast<int>( gridAdapter.cellCountK() ) };
 
-    if ( !deckFile.replaceKeywordData( "DIMENS", dimens ) )
+    if ( !deckFile.replaceKeyword( "DIMENS", dimens ) )
     {
         return std::unexpected( "Failed to replace DIMENS keyword in deck file" );
     }
@@ -204,7 +204,7 @@ std::expected<void, QString> RigSimulationInputTool::updateCornerPointGridInDeck
     // Format: NX NY NZ (use defaults for NUMRES (1) and  COORD_TYPE: 'F'=Cartesian)
     if ( std::find( keywords.begin(), keywords.end(), "SPECGRID" ) == keywords.end() )
     {
-        Opm::DeckKeyword newKw( Opm::ParserKeyword( "SPECGRID" ) );
+        Opm::DeckKeyword newKw( ( Opm::ParserKeywords::SPECGRID() ) );
         deckFile.addKeyword( "GRID", newKw );
     }
 
@@ -212,7 +212,7 @@ std::expected<void, QString> RigSimulationInputTool::updateCornerPointGridInDeck
                                   static_cast<int>( gridAdapter.cellCountJ() ),
                                   static_cast<int>( gridAdapter.cellCountK() ) };
 
-    if ( !deckFile.replaceKeywordData( "SPECGRID", specgrid ) )
+    if ( !deckFile.replaceKeyword( "SPECGRID", specgrid ) )
     {
         return std::unexpected( "Failed to replace SPECGRID keyword in deck file" );
     }
@@ -230,21 +230,22 @@ std::expected<void, QString> RigSimulationInputTool::updateCornerPointGridInDeck
 
     if ( std::find( keywords.begin(), keywords.end(), "ACTNUM" ) == keywords.end() )
     {
-        Opm::DeckKeyword newKw( Opm::ParserKeyword( "ACTNUM" ) );
+        Opm::DeckKeyword newKw( ( Opm::ParserKeywords::ACTNUM() ) );
+        newKw.setDataKeyword( true ); // needed due to bug(?) in OPM constructor
         deckFile.addKeyword( "GRID", newKw );
     }
 
-    if ( !deckFile.replaceKeywordData( "COORD", coords ) )
+    if ( !deckFile.replaceKeyword( "COORD", coords, true /*data kw*/ ) )
     {
         return std::unexpected( "Failed to replace COORD keyword in deck file" );
     }
 
-    if ( !deckFile.replaceKeywordData( "ZCORN", zcorn ) )
+    if ( !deckFile.replaceKeyword( "ZCORN", zcorn, true /*data kw*/ ) )
     {
         return std::unexpected( "Failed to replace ZCORN keyword in deck file" );
     }
 
-    if ( !deckFile.replaceKeywordData( "ACTNUM", actnumArray ) )
+    if ( !deckFile.replaceKeyword( "ACTNUM", actnumArray, true /*data kw*/ ) )
     {
         return std::unexpected( "Failed to replace ACTNUM keyword in deck file" );
     }
@@ -284,14 +285,14 @@ std::expected<void, QString> RigSimulationInputTool::replaceKeywordValuesInDeckF
         if ( result )
         {
             // Replace keyword values in deck with extracted data
-            if ( deckFile.replaceKeywordData( keywordStdStr, result.value() ) )
+            if ( deckFile.replaceKeyword( keywordStdStr, result.value(), true /* data kw */ ) )
             {
                 RiaLogging::info(
                     QString( "Successfully replaced data for keyword '%1' (%2 values)" ).arg( keyword ).arg( result.value().size() ) );
             }
             else
             {
-                RiaLogging::warning( QString( "Failed to replace keyword '%1' in deck" ).arg( keyword ) );
+                RiaLogging::debug( QString( "'%1' is not a data keyword, skipping" ).arg( keyword ) );
             }
         }
     }
@@ -1499,12 +1500,13 @@ std::expected<void, QString> RigSimulationInputTool::addOperNumRegionAndOperater
         if ( std::find( keywords.begin(), keywords.end(), "OPERNUM" ) == keywords.end() )
         {
             Opm::DeckKeyword newKw( ( Opm::ParserKeywords::OPERNUM() ) );
+            newKw.setDataKeyword( true );
             deckFile.addKeyword( "GRID", newKw );
         }
     }
 
     // Replace keyword values in deck with refined exported data
-    if ( deckFile.replaceKeywordData( "OPERNUM", operNumResult ) )
+    if ( deckFile.replaceKeyword( "OPERNUM", operNumResult, true /*data kw*/ ) )
     {
         RiaLogging::info( QString( "Replaced OPERNUM values for refined grid with dimensions %1x%2x%3" )
                               .arg( gridAdapter.cellCountI() )