Mind swapping/possession is not easy to implement.
The yithian mind swapped template is meant to be one way (since it assumes once a yithian gets hold of someone it is not going to let go
). Even so it has its limitations since it assumes a standard yithian is doing the mind swapping.
The problem is that there are to many variables to be set by a single adjustment. I think the best thing you can do it add an adjustment for each of the traits being swapped and handle each one individually.