add setter for NPCComposition

runelite-api/src/main/java/net/runelite/api/NPC.java

@@ -69,5 +69,7 @@ public interface NPC extends Actor
 	@Nullable
 	NPCComposition getTransformedComposition();
 
+	void setComposition(NPCComposition composition);
+
 	void onDefinitionChanged(NPCComposition composition);
 }

runelite-mixins/src/main/java/net/runelite/mixins/RSNPCMixin.java

@@ -102,6 +102,13 @@ public abstract class RSNPCMixin implements RSNPC
 		npcIndex = id;
 	}
 
+	@Inject
+	@Override
+	public void setComposition(NPCComposition composition)
+	{
+		setComposition((RSNPCComposition) composition);
+	}
+
 	@FieldHook(value = "definition", before = true)
 	@Inject
 	public void onDefinitionChanged(RSNPCComposition composition)

runescape-api/src/main/java/net/runelite/rs/api/RSNPC.java

@@ -9,6 +9,9 @@ public interface RSNPC extends RSActor, NPC
 	@Override
 	RSNPCComposition getComposition();
 
+	@Import("definition")
+	void setComposition(RSNPCComposition composition);
+
 	@Override
 	int getIndex();