Here is a picture with my test setup:
http://puu.sh/eeCnX/fcfd4fecf2.png
I just duplicated the Third Person SkeletalMesh and gave him a Red Material for testing. It’s name is “First Person” like you can see in the “Set SkeletalMesh” Node. Pressing K will change the Skeletal Mesh for me everytime i press it (because of the flipflop). For you that would be the Event Tick + Branch + “ThirdPersonState” Bool.
It’s all located inside the Character Blueprint.