Allow Guests to assign themselves, THEN limit what they can edit

We have contractors on a board that go out as they wish to complete assignments. What I would love is for them to only be able to edit things they are assigned to, without my team having to assign them. For instance, can we just add a feature where you can check a box to allow guests to assign themselves to an item? i have a series of automations that are in place for when the guest doesnt complete the assignment, which would then clear the assignee allowing for a new guest to assign themselves. It doesnt seem like that would be that difficult to add since the restriction is already in place. Just need one more, “exception” for an individual column under the current framework…