Cookies (the SIMBL version) is working perfectly for me (Dev Beta 3). SafariStand is loading but most of the options relating to tabs aren't working.
Anyway, to install SIMBL, remove all traces of EasySIMBL and then ...
https://github.com/norio-nomura/EasySIMBL/issues/26#issuecomment-117028426
When done, you can "ps -fe|grep -i simbl" and check the agent is running. Once installed, SIP can be re-enabled (it's a step in the above instructions anyway).
I have "Safari cookies.bundle" in /Library/Application Support/SIMBL/Plugins although it could well work in ~/Library instead.
Just to reiterate, I reckon this is an omission in DB3 (dunno about PB1) and should come back at some point.