Technically, WP doesn't support "changing" of a Planner's userID. However, if you want to user a different userID, you could create a new Planner account to use, and deleted the old Planner account. The drawback for this is that your assignments and memberships to teams will not follow you. In fact, they will be deleted once the "old" planner account is deleted.
Keep in mind, your userID is rarely visible in the WorshipPlanning.com. The two most visible places is the page listing all Planner accounts, and the Worship Flow for a service (in the Mod By column). The Mod By column can be hidden as per these instructions if you have the highest security level.