Just wondering, should a "minami-ke_okawari" tag be used besides the "minami-ke" tag. Because I think minami-ke okawari can be seen as a different anime. Any opinions?

No, see: post #180432

i dont think so. Its all minami-ke regardless.

The most interesting point about these animes is that the "two" different anime studios makes amimes based on the "same" comic.

its the same thing with negima, theres 2 animes adaptations and they both negima in here.

the diffences between negima! and minami-ke! is that for m-k, it still season 2 (even if it's made by an other studio), while in Negima! the second anime is an original story.