Cutting the stern wall of unused fuel tank compartment? ?

I agree with Half that as long as you don't go too big, an access hatch in the bulkhead would be OK. I'd go with a circular one, though, as usign a circle will help retain more strength in the bulkhead. A 6" pie plate would probably be fine - I might be hesitant to use an 8". Put it in the middle (vertically). And, yes, definitely re-glass the cut edge.
 
I agree with Half that as long as you don't go too big, an access hatch in the bulkhead would be OK. I'd go with a circular one, though, as usign a circle will help retain more strength in the bulkhead. A 6" pie plate would probably be fine - I might be hesitant to use an 8". Put it in the middle (vertically). And, yes, definitely re-glass the cut edge.
Even if you cut the hole in the bulkhead (which sounds difficult and a bad idea to start with) you'll still need octopus arms to service that pump through a small opening anyway. My advice is find a skinny kid that can follow instructions and wants to earn a couple bucks (if such a kid still exists anymore) and send them in through the live well opening and talk them through it.

I changed the pump in my 05 SF228 by myself last summer. I went in through the livewell and it took a few hours, sort of like a new form of yoga but wasn't that bad.
 
Even if you cut the hole in the bulkhead (which sounds difficult and a bad idea to start with) you'll still need octopus arms to service that pump through a small opening anyway. My advice is find a skinny kid that can follow instructions and wants to earn a couple bucks (if such a kid still exists anymore) and send them in through the live well opening and talk them through it.

I changed the pump in my 05 SF228 by myself last summer. I went in through the livewell and it took a few hours, sort of like a new form of yoga but wasn't that bad.
Time to join the Grady white Olympic contortion team. !