You can only remove signers that are pending or queued.

If you are using the API, remember to include existing pending and queued signers, otherwise, they will be removed from the signing list. You can add more signers to an order by including them in the request.

All signers have a priorityGroup value, where the lowest number (1) has the highest priority and vice versa. The default priority for a new signer is the current highest pending priority. The priority of a new signer can not exceed the highest pending priority.

GUI users can only change notification settings when creating the order, but API users can change the notification setting on the update signers request, by including the notifiyAllSigners: true in the option parameter.