"feel free to imagine whatever you want" still doesn't make something definitively canon, though. in a psl it's fine, but suppose you, a mod, let in Protag and Love Interest, obviously friends, who've decided that their headcanon is their characters got married at some point - something not supported by canon, though they could say it's not denied, either. you figure it only affects them and allow it. later, Love Interest gets swept in activity check, but Protag sticks around. a new player of the other character apps in.

i don't even need to explain how this is awkward at best and potentially godmoding at worst. if they'd developed that relationship more and gotten married after joining, that'd just be something the new player could ignore; but it's weirder if someone else's unsupported headcanon now contradicts their own characterization.

this is something that the mods of one large game asked a wol to change in their history, and for good reason.