Absolutely. You are most welcome to come in costume, but it must meet the costume criteria as set out in the Rules of Participation
For cosplayers there is a special entrance, where trained service will evaluate the components of your costume and their danger. Imitations of weapons (eg softened larp swords), non-functional weapons and even large suit bags are fine.
Prohibited items can't be bring in.
Inside is a cloakroom with changing cabins, mirrors and a first aid kit. More detailed information for fans with costumes can be found here