This is correct: neither CaveEditor nor Booster's Lab (that we have) can edit the major boss stats...
... Of course, the Lazerbear is a fetch quest and the Crestfallen spells have requirements... Infinity was posted already...
Crestfallen Cool requires talking to Mona Onederville (on floor 13, after Sonia Routen leaves) to get a corrupted doll... with that, a door on floor 25 leads to the (incomplete) Corrupted Code... trials await (including enemies based on Star Blocks)...
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Hm... a thought... is the Major Boss HP thing a Hackinator feature...?
Yes, the Boss HP can be altered in the Hackinator; it's found in the Boss Health section and alters the HP of major bosses. Come to think of it, perhaps Qwertyuiop could have special dialogue if the player obtains the Laserbear/Crestfallen Cool/Crestfallen Infinity?