Why would you need to link "all program files"? The only things I symlink are the Data and Interface folders.
Blame on my laziness. File copy is easy task, but....

I have 1 full sized folder that the main runs from. She runs at very high quality settings, 60+FPS, DX11 and all the bells and whistles.
1 folder for my healer. She runs at the same high settings, except she uses 30FPS and DX9.
1 folder for my other slaves. They run at low settings, no bells and whistles, DX9 and FPS capped at 20.
Indeed that is a good suggestion. /bonk myself for having individual folders for all

Anyhow, I have managed to rewrite my scripts to launch all clients from same folder, but with individual config.wtf. The rest of files under the WTF folders will still be shared by all. Conducted some tests, results seem good. No more copying of files after patch. Will continue to observe if there is any problem with this setup.

Thanks Khat and Mirai