Hello!
This project sounds very interesting! I believe that I could do it in very high quality, and that you will be absolutely satisfied with results.
What I plan to do If I get this project, is to first of all, recreate guitar in 3D, in very high detail and quality.
After that renders would be made in studio environment, with lighting placed in such a way that every little detail can be visible.
When renders are complete, photoshop work is quite straight forward... Smart object distorted to match shape of guitar, and all you will need to do is to import new design in smart layer, and it will be automatically changed on guitar itself.
This way results can be completely realistic, and changing design can be very fast.
I hope that you are interested in my bid.
If you have any questions, please, feel free to ask.
Thank you,
Yohatch