So this is what I tested. Search the summon hp, change all to value 1, activate it, deleted it. the value will stay 1 and won't crash if you click retry. I can farm this a lot faster since the first two waves are easy to clear.
How did you get the hp? I wanna find out the Crash Sephiroth's total hp
That's good if you changed all values to 1 and this stays for lot of fights (I will test later).
Usually I just changed to 1 the 2 HP values that really impact the boss HP.
To discover any enemy HP, it's easy. Just do a search for Unkwown value with the battle paused, then do any damage, pause again then search for decreased value until you find 1 or 2 values, this will be the enemy current HP.
Save those, and restart the battle so you have the max HP now. ;)