I have bought two overtree kits of the Bf 109G-4 overtree kits when the Royal Class of eduards wrong scale Bf 109 came out. By accident I had two sets of decals in it so I decided to keep my RC untouched (I got a 2nd one so that is no longer necessary).
Anyway a few weeks ago Eduard offered their new Bf 109G-6 kit as overtrees with an extra discount, so I too the opportunity to buy three of these. Two will be converted using the old Bf 109G-4 and one will be a Bf 109G-6 Nightfighter.
So first I cut out the egine panels along the panel lines with my trusty Hypercut saw. Horizontal from cockpit to rubber seal, vertical down, horizontal 2nd panel line above the exhausts and again vertical at the first panel line behind the spinner .. sounds more complicated that it is and I did not cae for the rest of the old donor kit. Next was the tail that I cut at the last panel line in front of the rudder. Both halfs glued together, not forgetting to add the tail wheel leg.
Same procedure at the new kit with focus on not ruining the kit where I want to keep it.
Worked out well though I was a bit impatient at teh tail and cut slightly into the fuselage. I have not pictures of these steps as I did that at some evenings over the past week while watching TV.
That might all sound pretty difficult but it was not and 15 Euro for a correction set is not that bad. I filled the remaining quarter circles as the tail cutting mistake with Magic Sculp. BTW both tails (old G-4 and new G-6) are equally long so that is no problem scalewise:

I also have the old "overlepty" for the G-4 and while it is a bit difficult to match the parts numbers (which differ from new G-6 kit and also from Royal Class instructions [sic!] ) I basicalle need instrument panel and seat belts.

Moving on to the wing I completed it without control surfaces and grinded out the position lights. These were replaced with Bondic (clear UV curing resin). A bit nerve wrecking as the stuff did not stick not well enough for sanding, so I lost one and hat to glue the others with CA .. it is not polished in the pic, so it looks a bit dull..

BTW one will get Jan Reznak's markings the other Viktor Petermann's .. but I am doing just one now.
all the best
Steffen