A: No. Cheat Engine requires a running process on Windows/Linux. You would need a physical GameShark or Action Replay cartridge.
A: Usually, no. But if you max all girls to Red Heart in Spring Year 1, the game might not know which cut-scene to prioritize. Advance events one at a time for safety.
However, wield this power with care. The best memories of Mineral Town are not of the numbers on the ledger, but of the moments in between. Use Cheat Engine to remove the toil , but never remove the heart .