Both "worlds" how can I do this?
 

Now that live EQ is free to play, is there a way to install it and play
without mucking up my "P99 EQ"?
Mostly I want to get back on the Test server some, where my best
guys ever were born and raised.
I'd try this on my own but I don't want to bork it up

You just need 2 separate installations of EQ essentially.

Sony usually wants to install EQ in a certain place, just be sure that your P1999 folder isn't the same place and there shouldn't be a problem with overlapping files etc.

If installing Live EQ causes problems because of your P99 folder, move the P99 folder onto a USB stick, install Live, then move the P99 folder back.

I'm not too articulate at this time of night, but I hope that made some sense :)