Vilas, yes the "strict interpretation" would have you adding the 5kt APP CORR to the 10 delta Vref. However, the ice is the same ice so the logical thing to do would be to just add the delta Vref 10 kts as it is the greater of the two.
You couldn't be criticised for doing it the way you suggest but if anything else went wrong you probably could be for doing the logical thing.
Another nail in the coffin of airmanship I am afraid.