You can replace any limb with a default limb, even if it's animated. We don't encourage this because it's a destructive action which can potentially lose hours of work, and so it's a little bit buried:
Select one or more limb layers, choose the type you want to replace them with in the Type dropdown, then hold Alt and click New. The limb layer will be replaced by a new default limb of the selected type, but the controllers, and all the properties in the Limber effect, are untouched. Any customizations that had been made to the original limb layer are not remembered during the replace operation.