CASA will probably be against your type of work, because you are working outside the scope of the schedule 8 maintenance limits!!
Pilot maintenance is only for minor items to keep the aircraft flying in an inspection sense.
Sanding skins, applying paint, all falls under the AC43.13A guide of standard practices. Are you using corrosion etch treatment of alumi-prep and surface reconditioning of alodine on the aluminium skins once you have sanded back the conversion skin coating? It's like taking away the anodized coating on a part. If not, then you are wasting your time, as the corrosion will just come back AND you are performing work NOT in accordance with the airframe maintenance manual, which becomes illegal if you don't follow the manufacturers recommendations. Also the type of paint used, both two-pack primer & solid base topcoat must be listed in the consumables manual or standard practices table listed in these approved paints by Cessna.
Basic answer is that you would be not following standard specs.
Easy solution is do it yourself, but be prepared for corrosion to come back, and always check with your issuer of your maintenance release that they are happy for you to do the work.
PS: Don't sand any rivet heads off !!!!!!!!!!!!!