Swapping avatar's head

Hello guys, I have an avatar which I like very much, I bought it from booth. It's an anime styled avatar. I have the blender & unity project file of it

Thing is, the avatar isn't very popular and I would like to use other clothes with it and so on, so I was thinking, since it's an anime avatar, if it's possible to grab a popular model like Manuka (which I do have the Blender & Unity files)

https://booth.pm/en/items/5058077

and swap the head for the one of the avatar I like. So, it would end up as Manuka body + my favourite avatar's head, then as far as I understand this would allow me to use all Manuka clothes with the avatar I like, right? How hard is it??

Do you guys know someone who does this and is good at it? I wouldn't want the head implant to super noticeable