Adding/Removing Assets on Asset Route on Work Order

We have a work order that was released last October, and is still in released status. We are on version 12.2.5.

There has been charges against the work order in previous periods that are now closed.

It has an asset route on it. The route is set up to allocate costs equally across assets. When we try to add/remove an asset on the route, we received a message that "Period for the work order is closed".

So are you not allowed to add/delete assets from an asset route with work order in status of released? Are you not able to because there are costs associated to the work order already in a closed period?