Are you talking about the Yamaha aftermarket skid plate with the threaded inserts you can drill out the old one and insert a slightly larger one and don't over tighten them. Once those threaded inserts start to spin there is not much you can do.
Or you can drill out the insert and replace them with a threaded C-clip similar to the one in the link below
I think that's it. I don't have the stock engine plate in placeall that's there is a thick plastic skid plate.
It doesn't fit the greatest and I ger snow getting packed in there.
Thanks for the response, I'll have to look at those nuts