In earlier versions of Limber, we had a Swap button which was later renamed Replace. We don't encourage this operation any more because it's a destructive action which can potentially lose hours of work and has too many caveats. But we have kept the functionality, slightly buried, for times when you really do want to replace an existing limb with a fresh, default limb, whilst retaining all the properties in the Limber effect.
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.