How to disable/delete a group

How to disable/delete a group

Hello,
 
I want to remove a group from the list of available groups for a specific site but I don't want to delete it, since I will lose all my history for that particular group.
 
If I delete the group the message "Can't delete because the groups is in use by another module" (or something like that) and I really don't want to go ticket by ticket change it to the new group.
 
When I try to rename the group, it changes but on the resolved tickets the new name appears when actually that group didn't resolve the ticket.
 
I hope I make myself clear. 
Please advice.
Best Regards,

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