Why are you wanting to "copy" user group permissions... they are cumulative. If you want someone to have "more" permissions, you simply create another group and enable those specific permissions in it and assign them to it as a secondarym (which is really a misnomer, since you can have multiple "secondary" groups)..
The only time I've seen anyone needing to "copy permissions" was when they were trying to shoehorn the cumulative permission ability of XF into a "standalone group with special permissions" that encompasses permissions set elsewhere (think IPS, myBB, SMF and such).