I'm my current game project my main character needs to transform into another character, i can easily change the mesh data from the gameObject, but i can't find any documentation about changing the Armature data for my Armature object.
If you are talking about Armature datablock, it is similar as changing the mesh data for mesh object:
If you are talking about changing Action Data for armature, there are two places to go, depends on your actual need:
For BGE action, you may take the 2nd one.
PS: Action Data exchanging between armatures requires high similarity, in other words, same hierachy, same bone count, same bone names, etc. Otherwise it will not work as expected.