Can I drill a hole for a screw in a connector?
Based on experience electricians say that the hole in the connector can be bigger than the bolt. So there is no problem to use a bolt M12 for a connector that was designed for bolts M16. Anyway, a bimetallic washer ensures proper connection.
There is no reason for making the hole in the connector bigger as it is a very difficult task and the size of the connector pam might be not enough. If you will make the hole too big it will influence the mechanical stability of the connection.