(~I'm not saying this is a good or bad thing, just different from how international fans enjoy kpop!~)
Often at music shows, you aren't allowed to cheer for other groups if you came with a fan club (which is how you have to get into the shows 90% of the time)
Some fandoms are more relaxed, but at the end of the day you should only be faithful to one group, you should only call yourself by ONE fandom name.
It might for international fans, but never Korean.
If you SWITCH fandoms or join a new one, you really have to switch. You can't suddenly love your old group and then also call yourself by the new fandom name.
Remember that Korean fans put a lot of personal time and money into the fandom. Buying albums, streaming to help the songs chart well, etc. Not that international fans don't do this as well, but in Korea its a big deal.
While I love sooooo many groups, the only group I really devote my time to is VIXX. Yes, I love BTS but I'm much muuuch more devoted to my 6 insane little VIXX kids.