I would just assume that this type of specialty dressing does not apply to the staff who are working with patients or any other serious endeavor. I think it's fine to have different "spirit" activities and would not want to hinder those who feel it is appropriate to their work-type. So I think the approach is to dress for your professional duties, and I'd not even worry a minute about when and how to add something--I mean that as, not worry. If it's convenient and you are happy to wear the necklace or similar later, great. On many days I don't have spare brain cells for that. Then I'd just interact collegially and compliment folks on their garb and plead that I had (patients, clients) today or whatever, but maybe next year!
I do get grumpy at plans for garb such as "ugly sweater" which is quite a bit more fraught those pink or red days, which are not so linked with being ironic, offensive or even looking like you don't know how to dress. In our hospitals, sure, there are people wearing reindeer headbands and Santa hats now, and there are witch hats in October, and scrubs with all sorts of holiday themes, and I enjoy them and compliment them, but thankfully no one is trying to declare that everyone in all areas should wear one type of thing without regard for the type of work and the people with whom we are interacting.
It may be harder in workplaces in which a lot of people are not in your situation that day and not as aware of the types of concerns, and are just thinking more business-casual-fun. So I'm sure they have the best intentions.
Bah!