Slick I have to ask you.
Would you expect to see this on a new installation?
This is the kind of repair that if I was an inspector would surly consider on an obsolete panel but would not consider if a new installation.
The fact that the panel cover had to be modified like this screams that something is not right.
The panel, the breaker, the cover....one or more of these items is not the right part and we should not be looking for a workaround.
No flames, just my professional opinion, Bob