How do you join two models together without messing up existing shapekeys? first time asking a question on here so I'm sorry if I leave anything out of my question.

Getting straight to the point, like the title says, how're you able to do that? In my case I have a Head Model that contains many shapekeys on it (like expressions). I just want to simply connect it to a body mesh/model without the shapekeys basically getting destroyed.

I've tried some common methods such as bisecting the body model around the neck and then bridge edge looping the head and body after joining - as well as going by each and every one of the vertices of the head and the neck and joining them that way. I mean, both methods end up looking nice after some smoothing but the shape keys I had on the head are practically destroyed and cause weird deformations (even around places that don't have anything to do with the original shape key).

Thanks for your time!
There is no problem in joining two meshes with shape keys: you only have to be sure that - before entering edit mode - the "basis" shape key is selected in both the meshes. If some shape keys share the same name, change one of them or they will be merged.
All Shape keys are retained as long as you don't modify the vertices moved by shape keys.

If a shape key moves some vertices that you want to stay still: select all vertices you want to stay in the "basis" position, Ctrl V "Blend from shape", in the left bottom corner of the "T" toolshelf panel select "basis" and uncheck the "add" option. This method works also for copying part of a shape key into another.