Got the drive and - gingerly - took the new drive apart, and hooray, it's the early 7201 model, meaning it has no write protection! I was able to reassemble the drive - which is difficult tbh, you have to put all the screws and such in just so - so now I have to never take that stupid thing apart again (until the drive belt inevitably breaks, which will be awful. The previous owner installed a clear belt, which hopefully lasts longer than the original black ones).
I do, however, have to mod the power supply board on my Twin Famicom, which is supposedly way simpler than modding the disk drive, but I'm sure I'll find a way to screw it up (or, more likely, not be able to find a guide for my exact model of Twin Famicom).