This is what I was going to point out and take one step farther. TBH I wouldn't mess with the playerslot file in terms of permissions because you'd have to unlock it every time you add/remove an alt. You're more likely to cause game issues that way. Yes, you can drag/drop and it's pretty quick. The trick with that is that the game sometimes scrolls too quickly, so it takes practice. Now that we get a billion slots (10 per page) it's possible to sort/group your alts if they're themed in some way. I haven't tried using comments in the file, but since it's based on C/C++ I'd assume that you could comment with group separations like Hero, Vill, etc.
As for editing the file, no, you don't have to rearrange the order, but it would make your life so much easier if you're looking to arrange them using it. Since we can copy/paste with ease, then it's just that simple to make a new file, setup the numbering, and just copy/paste the names.