Hello! ^_^ Thank you for your time and questions. To answer your questions:
A face claim is a person you choose to play as your character in a book, roleplay, video, or anything related. It's an easy way for you to not have to describe your character or for people to imagine what your character looks like. Also, it doesn't have to be a real person either. It can be anime, cartoons, game characters, or drawings. Many people usually just use celebrities and models, as their face claims.
RCTA means 'race change to another', and ECTA is short for 'ethnicity change to another'. When people use rcta or ecta, that means they want to be identify as a different race or ethnicity than the one they were born with and their country. Another term is CDTR, which means 'change to desired race, and CDTE means 'change to desired ethnicity.' Some people change their race and ethnicity for various reasons, but most of them don’t feel connected to the race, ethnicity, or culture they were born with and feel more aligned with another one. However, all of these terms are becoming problematic and controversial, as some are claiming they're a form of racism and fetishization of certain cultures. It all depends on how you view it.
Face claims have existed way longer than RCTA and ECTA. There are not the same things. Hopefully, I was able to give you the answers you were looking for. Also, you're not bothering me at all, and feel free to ask me any questions. I'm not the best at explaining things, but I will try my best. :)