How to change topic numbering behaviour in an existing map when a filter is applied

I have an existing map which was created with the option unticked for new files to renumber topics after a filter is applied. Now I want this option to be applied so that topics are renumbered dynamically whenever a filter is applied or changed.

Obviously ticking the box to enable this under Filter options in the global options menu does not change the numbering behaviour in an existing map. I'm sure there is a trick to do this for an existing map but I can't find or remember it.