The current policy is to have only one livery per pilot per aircraft module. When there are two modules in game such as DVII and DVIIF you can have one each.
This was implemented in order to keep the Paint Pack size down.
Because of the greatly reduced number of active pilots, maybe we should talk about amending this but that would need a JG1 Command decision.
Personally, I like the idea of showing a progression of paint schemes for a particular pilot. Didn't MFR have several variations for his Alb DII (or DIII)?
From the Dicta PaintPolicy:
Basic Standards
2. All JG Nr. I pilots, who are full and active members of the squadron, are entitled to have one personal paint scheme added to a paint pack for every German aircraft flown by the Unit.
Reading this would imply that a pilot can have several skins per aircraft from any other 'air force'. Removing the German seems the simplest solution.