Did my friend F**** up?
 

Have a buddy who picked up a FC he believed was flooded, for some reason or another he pulled the leading plugs out but left the wires to his trailing plugs in and proceeded to turn over the motor... Full ignition and all. He said he heard a loud bang, and that's when he realized he did something wrong and called me. My question for you guys is could this have been detrimental to his engine? 87 base I believe, with a 6 port N/a thanks in advance

put the plugs back in,hook up the wires and find out.
What he heard was the trailings igniting the fuel..

I understand that, I'm just verifying it couldn't have had an effect on say an apex seal or any other internal seal for that matter.

Its possible, never know. Pull the plugs roll it over and listen, or comoression test it

Never done it, but I doubt any damage was done. With the leading gone, I don't see combustion pressure rising high enough a hard seal would be threatened.
I might chase the plug thread once just for giggles to make sure it wasn't fouled with carbon blowing out. Make sure you use some anti-seize on the plug thread when it goes back in and proceed.

There should be no issue.

This is how I diagnosed a bad injector on an FC some months back. Pulled leading plugs and cranked engine. Front rotor shot flame out of leading hole every rotation, rear rotor did not. No fuel to rear rotor.

Incidentally turned out to be a bad connection at the solenoid resistor. Who knew?