Yes. That would be a good option. I think without characteristics it might give an inconsistency error in the plan.
Another similar option would be to create two 01 inspection types. For one of them turn off "insp. with charc." indicator. The use the user exit to select the correct inspection type based on a flag for for the vendor. Possibly a characteristic in vendor classification.
Then you would only be able to do usage decision for the one inspection type, no results recording even though the same inspection plan is used in both cases.
Craig