Context Menu Maintenance is probably what you’re looking for. For the two examples you have listed, you’d be looking at the Customer.CustID and probably CustCnt.Name for the other.
Once you know the appropriate Process ID’s you can either restrict them and/or add your desired customization through Menu Maintenance.
Ah, yes. As luck would have it, both forms you are describing are subforms. These are both variations of Customer Maintenance (OMMT1110). That complicates things a bit. I suspect there is some Epimagic at play here where subforms are automagically included.
Subforms can be customized though. You can find a discussion on that here: