Yes, you can install any exe by:
- Launch PlayOnLinux
- Click Configure
- Select Baldur's Gate virtual drive
- Click Miscellaneous
- Click "Run a exe in this virtual drive"
- Then navigate to your downloaded exe
In your case, download the Fix pack, BGT-WeiDU, Unfinished Business, tweak pack, etc
Then extract them with archive manager to your desktop.
Follow my instructions for running an exe and navigate to them on your desktop.
Now there is a chance they won't work in Linux, but its worth a try.
I have installed mods for several games and they worked fine!