Now that's a fault i'm very familiar with [end of drum wiped off] by an errant chain stacking in there. I fixed many many at work on farm bikes Ag100--Ag175 LT/CT type motors by drilling straight in & tapping to 6mm with a washer, & can still get the three screw cover over it albeit likely one screw hole will be broken out.
If the drum moves over [which it will as becomes floating] you can end up with 'bad things happening'--dogs running into dogs [umm-dog knotted]. Nor 100% convinced it would lock the lever solid--but!!. Besides riding it would show erratic running in the trans. I dunno, was 45 years ago when we had that problem with total lack of maintenance by the farmers & knee deep in mud & cow s#$t until chain came off.

Gotta show this to YAMFAN. One of our experiments haha. Go where no horse or trials bike would--well in theory lol.