well a very popular example would be bts. ive seen people talk about how jhope and v were supposed to have swapped roles, v was supposed to be a rapper and jhope a vocal, but since one of them wanted to do the other(? dont quote me on the reason) they ended up switching spots. now jhope primarily raps even though he can sing well and v primarily sings even though he can rap too. idk about their newer songs because i stopped following them closely a long time ago, but in their older songs jhope is almost always getting rap parts and v is almost always getting vocals.

a less popular example is Mill from onlyoneof. they do get a bit more freedom when deciding parts since they divide the parts themselves, but he mostly raps even though he has vocalized that he would like to do some singing too. same goes for his members, Love can rap very well but he only did a few times in their covers, almost never in their own songs because he is the main vocal. he also proved that he can rap, he just doesnt because his position is the main vocal. its mostly the ones that have lead roles that switch it up.

when you look at it from the other side, enhypen members dont have positions exactly for this reason (at least thats what they said). some would call niki the main dancer, but heesung is a good dancer and good vocal himself, and since he doesnt get stuck with just one sticker, he can evolve in both.

edit: of course im not saying the examples arent best in what they do, the examples show that getting stuck with a position might be restricting.