If I use the bhaalspawn powers "patch" provided here, will installing any other mod remove it? Because I noticed that the AR4500.bcs file seems to change size when another mod is installed.

I added the Bhaalspawn powers patch before a fair few other mods. When I finally got to the pockt plane, I still got extra powers from the Trials. I don't think installing other mods is a problem.

If you install the one found here before WeiDU mods then there's no problems. Non-WeiDU mods may overwrite it, whereas WeiDU ones will just add to the top or bottom of it.