When adding a standard operation to the routing you can add it either as a reference or copy. If you add it as a copy you can freely change the operation on the routing, but if you want to have it as a reference you cannot change any values on the routing. You should change it on the standard operation and propagate the change to the routings where used.

The reference and copy feature when adding standard operations resolves this issue. If you want to prevent removing you could set it as reference.