How to capture event right after copy from or copy to

Hello Expert:

    Need to do some value changes for a fields that only exist in Credit Memo's. If it is manually created, then it is not too bad. But if it is copy from or copy to. I can not find the right event to capture it. just before user start final edit or ready to add.

    I have tried the form.getfocused but doesn't seem to work. Field customer name is always in focus after copy to, But capture that field.getFocus doesn't seem to be working either.

Any ideas?

Thank you

Bo