Installing a Helicoil involves drilling out the damaged threaded hole, tapping it with an oversized thread, and then threading in an insert that matches the original thread. Easy process, but I'd remove the cover if you can, because:
- you don't want the drill shavings ending up in your motor
- crouching down beside the bike and craning your neck while drilling and tapping isn't just uncomfortable, but also asking for something to end up crooked
That said, I had to repair 6 valve cover holes on my basket case RXV, and I wasn't going to remove both heads, so I taped everything off and drilled slowly with a vacuum to suck up the shavings as I went. The holes didn't go straight through, so no issues with them actually falling into the heads. I also used a jig/guide to keep the drill bit and tap as straight as possible to the hole surface, since I was working on the heads at their natural v-twin angle.