My apologies for a bit of a bump, but I was bothered by this feature years ago, too. I used the info from this thread to change the button from A to B in FE6 and 7. I chose B because it allows you to control the speedup at your command while never activating it by accident and still being able to see the targeting cursor on enemy phase. And if you want to skip that enemy cursor, just hold both A and B.
FE6: . 0x060E28 change 0122 to 0222
FE7U: 0x06D466 change 0122 to 0222
FE8U: 0x0794F6 change 0120 to 0220 (untested, theoretically true)
I’ve still yet to start a project on FE8, so I never made the edit there myself. I looked at the assembly just now, though, and what I listed makes the most sense.
The thread I linked also lists how to disable the game completion requirement. It doesn’t list FE6, but l wrote down something that I came up with myself:
“changed 0x060E1E’s comparison to 0000 0000”
I know I have it working on FE6, so it only makes sense that’s what I did since I have it in my notes. It’s what I’ll try if I need to remove the completion requirement from a new ROM, anyway, so I think I’d trust it. (Still gonna slap my past-self for not leaving better notes)