You did such a good job on the port side flap that the camo looks better with it
In short it’s unlikely RA ground crew *repainted* the rear fuselage, they didn't have access to German paint stocks until 1944, and nor did ground crew apply a spray of GAC1 over that area, especially on a plane that was meant for training. I believe the white band was already present on these planes (F) but your question can be answered in three parts:
1) 15 x F4 - old machines built in 1941 mostly drawn from German units in Greece (Mediterranean theater) JG.27. Deliveries began on 19 April 1943
2) 6 x G2, 10 x G4, 91 x G6 - built between Feb.-March 1943 - (relatively) new/new
3) 6 x G2, 10 x G4, 91 x G6 - built between Feb.-March 1943 - from existing German units
Notes:
1) The F4s that were drawn from German units in Greece can be assumed to have had a white fuselage band, applied by German ground crew. The width and placement of the white band didn't seem to follow any order as seen by the first two photos below (Bf.109F) - ref. Squadron Signal Pub. #57. In the first photo, the bands are different width and located on different parts of the fuselage and the plane in the background, the fuselage band is applied at a slight diagonal. In the second photo, the plane furthest from the camera, the white fuselage band is quiet wide while the plane closest to the camera is narrow - again note the placement of the bands relative to the Balkenckreuz. The third photo shows a Bf.109G with no band. Note that 150o Gruppo
G6s all seemed to have had a uniform white band 600mm width at the same location on the fuselage which suggests most of these planes were received by the RA with no fuselage band or some were new.
2) These planes were received from factory or transferred to the RA in a new state without a fuselage band. The fuselage band was applied by RA units uniformly 600mm width at the 5 panel, overlapping 4 and 6 panels.
3) Planes that came with or without a fuselage band.
There is a RA Bf.109 where German markings extended slightly further astern and were repainted with GAC1 and the white band applied over GAC1 Bf.109G6 4-154 W. Nr.18096. I only have the profile of this plane (below) but the photo is in D'Amico's first book on the subject. This plane was received either new or without the fuselage band. In Ali Straniere #1 there's a good list of all known Bf.109s received by the RA and ANR and you can see which were received from existing German units and those that were probably new.
In regard to the plane you're modelling, I believe a white band was already present on this machine and its width was approx. 600mm from the photo I posted above. Also in the photos below, German Bf.109F units operating in this area (JG.27) didn't carry codes on the rear fuselage or aft of the white band. Without a photo of the rear fuselage of this particular machine, I would leave your model as is (maybe Stefano has more to add here).
