People have been launching multiple game clients from a single folder for quite some time now. The main
reason people were launching from separate folders was if they wanted separate config.wtf files for each
of their characters. It's actually faster for the disk to read what it needs to read from one folder versus
multiple folders because of disk caching and queues.

The only writing to any files should be (quickly thinking off the top of my head):

1) Cache folder. If you've cleared your cache for whatever reason I would recommend launching one client
and letting the cache rebuild itself a bit so you aren't trying to write to the cache directory 4, 5, 10 times at
once. Otherwise, your cache folder is only being read.

2) Config.WTF file -- ISBoxer's file virtualization fixes that problem but, I don't know what HKN has to offer
along those lines since I'm not savvy with the software myself.

3) Add-on Lua files. 90% of add-ons should be character specific through profiles and those add-ons that
aren't (that I've come across) are usually kept the same on all clients anyway.