Hey, now HERE'S a weird question.
By default, every time you start up the game, the Mii list on the character select screen is sorted by the most recently created/edited Miis. If you go into Games & More > Custom > Mii Fighters, and then sort the Miis to "By Type" or "Last Used" instead of "Order Made," they'll also arrange in that fashion on the character select screen as well!
But, like your game settings (like when you set it to stock instead of time), every startup of the game, this resets.
I wonder, then, since you can mod stock or coin to be default on startup instead of time, could we mod the Mii list to sort to Last Used or By Type on startup? As silly as it is, and maybe not crazy useful to most people, I'd really like to do it for myself! But I don't even know where I'd begin to look. I'll have to poke around in the global parameters I guess?