[New Joe]

Go into 'UserGroups' in your admin cp
Click on 'Add new UserGroup'
At the top base permissions off 'General UserGroup'
Give it a new name 'No repo UserGroup'

Then fine' User Reputation Permissions'
And disable it there.

Although, that user group will still be able to 'receive' repo
I didn't read that part of your ask until I'd typed out the above.

Well now I get you, it actually sounds like a modification that should be make, the action of not being able to use it is there in the vB core but it doesn't stop another user group from giving you repo.