I've had that dilemma myself. I decalled one model myself (an ATA 737-800) for fleet-building simply by changing the regstration number. I also decaled an Overseas National Airways DC-8-21 (tail only) with custom decals that V1 decals made for me. These were very easy to do. I did also decide to make a custom American Trans Air 707-323C and also an ATA 757-23N in the "vacation" scheme. These I decided to have custom-made for me (I have zero experience disassembling and repainting 1/400th scale models). The results were great, and I am so glad I went this route rather than trying to do them myself. The prices were very reasonable..US $100 each including shipping, I supplied the donor models.
My personal advice, if you want it, is that if it's a simple decaling job, and you have experience working with VERY small decals...go for it. For a complete repaint and decals; if you have experience with disasssembling and painting 1/400th scale models, give it a try. If you have any doubts (like I did). have them commisioned. I hope that helps at least a little.
I do have photos of all the models that I mentioned. The ATA 737-83N N332TZ, I simply removed the N301TZ registration from the Gemini Jets model, and used decals made by Draw Decal for the new tail number.
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For my Overseas National DC-8, I had V1 decals make a custom decal blue stripe with 2 white stars to cover up the ONA titles to make N1976P match after the travel club Club USA purchased the aircraft for use based out of IND from May 1978 unttil mid-1980.
The prototype before purchase by Club USA:
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The prototype after purchase by Club USA:
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The model with the tail decals applied:
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As for the customs that I had commissioned, American Trans Air 707-323C N8416 on an Aeroclassic mould:
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And finally, ATA 757-23N N514AT in the "vacation" scheme on an NG mould:
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