The least disruptive way is to create a second account, send that account a join link. Join with the character, then kick it. That will regenerate the join link so no one can enter using the old link. Everyone currently in the campaign will still be in the campaign - they wont be affected. As a GM having a second account is handy for checking out how things look from the player point of view, and testing things as a player. So it's beneficial to have that second account anyway.
