diff --git a/CHANGELOG.md b/CHANGELOG.md
index 724a60e..20197e2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,4 +1,9 @@
-# 4.1.0
+## 4.2.0
+
+- Fixed Solana simulate transaction model
+- Added helper methods to solana versioned messages for replacing blockchains
+
+## 4.1.0
 
 - Fix Solana pre-instruction serialization issues
 
diff --git a/lib/solana/src/rpc/models/models/simulate_transaction_response.dart b/lib/solana/src/rpc/models/models/simulate_transaction_response.dart
index d104978..b086df1 100644
--- a/lib/solana/src/rpc/models/models/simulate_transaction_response.dart
+++ b/lib/solana/src/rpc/models/models/simulate_transaction_response.dart
@@ -20,9 +20,9 @@ class SimulateTranasctionReturnDataResponse {
 }
 
 class SimulateTranasctionResponse {
-  final String? err;
+  final dynamic err;
   final List<String>? logs;
-  final List<SolanaAccountInfo>? accounts;
+  final List<SolanaAccountInfo?>? accounts;
   final BigInt? unitsConsumed;
   final SimulateTranasctionReturnDataResponse? returnData;
   final CompiledInnerInstruction? innerInstructions;
@@ -31,7 +31,7 @@ class SimulateTranasctionResponse {
     return {
       "err": err,
       "logs": logs,
-      "accounts": accounts?.map((e) => e.toJson()).toList(),
+      "accounts": accounts?.map((e) => e?.toJson()).toList(),
       "unitsConsumed": unitsConsumed?.toString(),
       "returnData": returnData?.toJson(),
       "innerInstructions": innerInstructions?.toJson()
@@ -49,9 +49,10 @@ class SimulateTranasctionResponse {
     return SimulateTranasctionResponse(
         err: json["err"],
         logs: (json["logs"] as List?)?.map((e) => e.toString()).toList(),
-        accounts: (json["accounts"] as List?)
-            ?.map((e) => SolanaAccountInfo.fromJson((e as Map).cast()))
-            .toList(),
+        accounts: (json["accounts"] as List?)?.map((e) {
+          if (e == null) return null;
+          return SolanaAccountInfo.fromJson((e as Map).cast());
+        }).toList(),
         unitsConsumed: BigintUtils.tryParse(json["unitsConsumed"]),
         returnData: json["returnData"] == null
             ? null
diff --git a/lib/solana/src/transaction/core/core.dart b/lib/solana/src/transaction/core/core.dart
index 4856a2d..1c3ae7f 100644
--- a/lib/solana/src/transaction/core/core.dart
+++ b/lib/solana/src/transaction/core/core.dart
@@ -39,6 +39,13 @@ class TransactionType {
 
 /// Abstract class representing a versioned message.
 abstract class VersionedMessage {
+  VersionedMessage copyWith(
+      {MessageHeader? header,
+      List<SolAddress>? accountKeys,
+      SolAddress? recentBlockhash,
+      List<CompiledInstruction>? compiledInstructions,
+      List<AddressTableLookup>? addressTableLookups});
+
   /// The message header, identifying signed and read-only [accountKeys].
   abstract final MessageHeader header;
 
diff --git a/lib/solana/src/transaction/message/legacy.dart b/lib/solana/src/transaction/message/legacy.dart
index 846c413..85d03b7 100644
--- a/lib/solana/src/transaction/message/legacy.dart
+++ b/lib/solana/src/transaction/message/legacy.dart
@@ -30,6 +30,21 @@ class Message implements VersionedMessage {
     required this.compiledInstructions,
   });
 
+  @override
+  Message copyWith(
+      {MessageHeader? header,
+      List<SolAddress>? accountKeys,
+      SolAddress? recentBlockhash,
+      List<CompiledInstruction>? compiledInstructions,
+      List<AddressTableLookup>? addressTableLookups}) {
+    return Message(
+        header: header ?? this.header,
+        accountKeys: accountKeys ?? this.accountKeys,
+        recentBlockhash: recentBlockhash ?? this.recentBlockhash,
+        compiledInstructions:
+            compiledInstructions ?? this.compiledInstructions);
+  }
+
   /// Constructs a message from a serialized buffer.
   factory Message.fromBuffer(List<int> buffer) {
     return SolanaTransactionUtils.deserializeMessageLegacy(buffer);
diff --git a/lib/solana/src/transaction/message/message_v0.dart b/lib/solana/src/transaction/message/message_v0.dart
index a4c7329..6c01bcf 100644
--- a/lib/solana/src/transaction/message/message_v0.dart
+++ b/lib/solana/src/transaction/message/message_v0.dart
@@ -34,6 +34,21 @@ class MessageV0 implements VersionedMessage {
     required this.addressTableLookups,
   });
 
+  @override
+  MessageV0 copyWith(
+      {MessageHeader? header,
+      List<SolAddress>? accountKeys,
+      SolAddress? recentBlockhash,
+      List<CompiledInstruction>? compiledInstructions,
+      List<AddressTableLookup>? addressTableLookups}) {
+    return MessageV0(
+        header: header ?? this.header,
+        accountKeys: accountKeys ?? this.accountKeys,
+        recentBlockhash: recentBlockhash ?? this.recentBlockhash,
+        compiledInstructions: compiledInstructions ?? this.compiledInstructions,
+        addressTableLookups: addressTableLookups ?? this.addressTableLookups);
+  }
+
   /// Compiles a version 0 message from provided parameters.
   factory MessageV0.compile({
     required List<TransactionInstruction> transactionInstructions,
diff --git a/pubspec.yaml b/pubspec.yaml
index 64fcb6d..5460dad 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,6 +1,6 @@
 name: on_chain
 description: Streamline Ethereum, Tron, Solana and Cardano operations. Effortlessly create transactions, interact with smart contracts, sign, and send transactions.
-version: 4.1.0
+version: 4.2.0
 homepage: "https://github.com/mrtnetwork/on_chain"
 repository: "https://github.com/mrtnetwork/on_chain"
 Author: mrhaydari.t@gmail.com