Technical Issue: The Sims 3 Settings Menu Crash
xooIzzy I don't think it's a problem at all to have different settings for different saves, as long as you can keep them straight. I personally keep different Sims 3 folders for different saves because in addition to adjusting the settings, I also use different Store content depending on the theme of the save. (Dragon Valley doesn't need modern furniture or decorations; Appaloosa Plains doesn't need medieval or fairy-themed content.) But that's not the only way to do it.
What might help you is keeping multiple Options.ini files in a separate folder, renaming them to indicate which save they're for, e.g. Options-X family or Options-Y world. You'd copy the right file to your user folder when switching the saves, leaving the original where it is, then delete the copy and copy over another when you switch again.
This serves two purposes. One is that if you accidentally forget to change the settings for a new save right away, it's possible to confuse the game as to what aging settings it's supposed to be using, and sims might get stuck aging. (This is not a frequent problem but is absolutely possible.)
The other is that when your computer's graphics driver updates, the game will detect the new version and wipe the Options.ini file, reverting everything to default settings. You can fix this, once you realize it, with a backup copy of the file. Copy the lastdevice string (this lists the driver version) from the new Options.ini and use it to overwrite the string in your backup copy of whichever Options file you want to use. Then you delete the wiped Options file and replace it with your copy that has all the correct settings and now the correct lastdevice string as well.