Is that replacing or as well as it taking compressed air cells straight out of your inventory?
Autoconsumption isn't realistic and not interesting. Two ideas:
1) If we want it to be simple, then refilling can be performed with place an aqualang and ah air cell on a crafting table
2) ANother way is to add an oxygen tank, the item which contains comnsumable oxygen. Refiling an aqualang is performed by placing an aqualang and a tank on a crafting table, and result is like switching tanks - aqualang is filled with as much oxygen as was in the tank it was combined with and a tank filled with as much oxygen as was in the aqualang before switching. The oxygen tank can be refilled with a compressor.
I'd vote for the second one.
If the hat requires power for a light/see easier underwater, I'd rather have a batpack on or something, unless you leave the taking inventory air cells to the hazmat suit.
Oxygen or power But power cells can be changed in place