No. Blessings aren’t magical incantations. They’re prayers, prayed by priests, on behalf of the people who use the object in question.
The object coming into contact with pagan or unapproved objects cannot possibly cause these prayers to lose their effect. If a priest blesses a scapular that comes from an unapproved apparition, the blessing is still effective, even though the other rituals associated with that scapular might not necessarily be recommended.