Currently I am trying to make a coh2 mod for my friends and there are somethings I really don't know how to do so I am gonna ask some questions about coh2 modding

Question 1:
How do I change unit models (What i mean by this)
I am not talking about changing the unit model to a custom model because that's impossible in coh2 modding what I am talking about is changing the model to a different model like for example changing PanzerGrenadiers to american riflemen infantry models
Question 2:
How do I remove upgrades when I've already done one upgrade (What I mean by this)
For example let's say I have an upgrade called "remove battle phases" let's say when I click that upgrade it removes the battle phases and gives me new stuff in the wehrmact headquarters
Question 3:
How do I make it so pioneers or the certain starting unit of a faction despawns
for example pioneers don't spawn when you become wehrmact until you produce them
Ending:
If anyone could answer these questions I would really love that thank you if your reading this