You fit a fuse on the positive battery power lead to the electronize.

Yeah, it's just a straight swap. You have to desolder the relay which can be a pain then solder wires the holes left over, these lead out to the two relays that you are best mounting onto the plastic housing outside.

A featherweight would never be able to put 3.5hp into the ground unless it has magnets and even then, the motors will likely burn out before any meaningful time has passed.