I'm just finishing up my 80e & wiring swap but I'm waiting for my tuner with hp tuners 80e segment swap. My question is can I start my truck with current tune (60e), shift through gears and fill trans with correct fluid amount? I don't want to ruin this trans.

 

It'll be in limp mode (3rd gear)

You can crank it and get to operating temps to get fluids close. As long as it isn't a fresh rebuild i dont see an issue with just it "idling" an not being put into gear until the OS is updated.