Can I convert my surefire p6's to rechargeable batteries instead of 123?
I have 3 of the older lights with Led bulbs and it would be nice if I could use rechargeable in them

Yes, you can use RCR123's, or you can source a 16650 Li-Ion battery and use that if your 6p is an LED. Using the 16650 will probably void your SF warranty if that matters. I use a 16650 in my 6p pro, and it works just fine.

You can also have the 6P reamed out for 18650s.

For my Surefire E2D I've moved to 16650 batteries, which I'm also using in my G2 as well.  Run time is slightly reduced but not by much 2500mAh vs 3000mAh for primaries.  Here is where I purchased my batteries from, I already had a 18650 charger from my Surefire Peacekeeper so I just using it to charge my 16650 batteries

http://www.orbtronic.com/16650-li-ion-battery-rechargeable-protected