I want to turn off the rear o2 in the periphery bits. What will this do? Pros? Cons?

 

wont do anything, mine has been off for 7 months now approx 10K kms.

 

Will it get rid of my pesky TEST PIPE Check engine light

 

yes

 

It will turn off the heater also, so make sure you remove the actual sensor before doing so or it will be ruined. I believe you also still need to run MrFred's code (if applicable to your rom) to prevent a CEL for the heater.

Alternatively, you could run the code for the rear O2 sim or a tephra rom that already has it built in.