Anodizing is just a controlled corrosion, somewhat along the lines of gun bluing on steel. There is no reason to avoid painting it. First, wash with detergent, rinse and dry; then wipe down with acetone, naptha, or some similar solvent to remove all traces of wax. Ideally, you should roughen the surface with a scotchbrite pad (avoid wire brushing or sandpapers with any metal oxide content, they can embed metal particles in the aluminum and accelerate oxidation), Do this AFTER you wash and solvent clean, so that you don't work wax into the metal, then wash again. A zinc-rich primer is a good idea with aluminum, followed by a high quality topcoat that is compatible with the primer. A gray paint chosen to be a close match to the original mast anodizing will give you a like-new mast and no one will know you painted.
Ideal pre-treatment of aluminum involves "acid etching" bare aluminum with dilute phosphoric acid to help paint adhere properly, followed by treatment with "alondine" which converts the bare metal to help with corrosion proofing. These steps are likely not needed on an old weathered mast. See
www.aircraftspruce.com if you want all the info about painting aluminum.
