Without an NPC server, there is no means for any player to directly alter the values of another player. You would have to use save[] in some manner to get the other clients to see a requested change and make it themselves. Maybe some of the additions the Graal Reborn server has might be useful too, but I don’t really know anything about them.
Oh, thought I answered this.
It worked perfectly, thankfully we already had an invisible npcw owned by everyone.
But it seems it doesn’t work for npcs (only for players?) so I used callnpc with saves and global variables instead for the doors I scripted afterwards (and posted on “is this. serverside?”). It looks nicer anyway.