When the Compact Filter first arrived, there were a lot of threads on the forum about people trying to fashion homemade pre-filters for them. I didn’t have one, so I didn’t pay a lot of attention and don’t know how that worked out, but they could probably be found with a search.
When the redesigned Glowforge Air Filter was announced, Dan mentioned that it would support a pre-filter, and that they were “planning to work to make the improved cartridges and prefilters backwards compatible”. So it’s possible that at some point you will be able to get a new part that extends the life of your cartridge.
Finally, in my opinion, I don’t see Glowforge ever supporting the option for you to open the cartridge up and put in new filter material. I can think of a number of reasons why this seems unlikely, from their historical position on DIY maintenance to the potential liability when the filter no longer meets its advertised specifications.