When it comes to referring to the people who wear clothing or costumes, there are a variety of synonyms that can be used instead of "costumers." One option might be to use the term "dressers," which refers to individuals who wear apparel in general. "Wearers" is another option, as is "attire-clad individuals." "Garment-wearers" could also be used, as could "dressed patrons" or "clad customers." Other possibilities include "outfit-wearers," "fashionable individuals," or simply "those wearing costumes." Ultimately, the specific synonym used will depend on the context and the desired tone of the communication.