SCUBA gear definitely helps! However, I believe that you ought be 'grandfathered' on the illegality of your old cover. (even if you're not, the compliant covers fit the older drains)

Replacing the cover is very simple, all it is are the 2 screws that need to be removed, so you can get the rest of the old cover off and then reinstall them on the new cover. With SCUBA gear, it'd take < 5 min., without, you're probably looking at 20 min, (depending on the water temp and how long you can hold your breath.