Removed the evap canister from my 1985 XJ6 VDP to see if I could rebuild/replace the charcoal in it and yes you can.

The top "cover" is glued on and will need to be carefully persuaded to come off. I broke the glued top free from the canister by slowly working a small screwdriver under and around the cover's lip. On the inside of the canister will be the charcoal media and two screens, the one screen with the two holes fits in the bottom, obviously. I replaced the charcoal with some activated charcoal sold on Amazon for purifying water in a fish tank. I initially bought two 310-gram packages, but ended up needing a third, so all total I used 930 grams or 2 pounds of charcoal. Once the third order of charcoal arrives, I will top off the canister, fit the top screen, glue the cover back on and reinstall.