This is a problem I've been having for a bit when I started going just /opt blood 0 to hide the blood particles but to keep the bloodstains visible, which I check with /opt bloodstains. When I restart the game, the blood particles come back. Is there any way I could save those changes?

What is your game client version? You need a Steam version of the game or Toribash 5.51 standalone to be able to keep blood option stored between game sessions.

Alternative is using a shortcut to your toribash.exe with -blood 0 launch option.

ver5.5