Creating fixed width numerals for fonts missing this feature

While many fonts now have support for both proportional and fixed width figures, some of my clients are using fonts that do not support this functionality. I use Fontself to create a numbers only version of the font that has fixed widths for all the numerals. Then in InDesign I create a grep style that automatically replaces the default figures with my newly optimised ones. Usually only do this for the table figures as this is where it is most desired. I may be infringing on copyright issues here but as it is just a fixup for specific client annual reports and I am not getting any financial benefit from it I don’t expect it to come back and bite me. Maybe I should reach out to the original designers for permission to do this for the future.