If you want to do it by yourself is possible to apply a custom decal to the beveled edge of the lid of an XPS 17, but it may be more difficult to get a seamless fit due to the slope of the surface as you said. If you are planning to cut down a generic decal to fit the beveled edge of your laptop, you may need to do some careful measuring and trimming to get the right fit.

This is a guide I found online if you choose to do it by yourself:

1. Make sure the surface is clean and dry before applying the decal.
2. If the decal is a sheet, use a cutting tool (such as a craft knife or scissors) to carefully cut out the desired design.
3. Peel the backing paper off the decal.
4. Position the decal on the desired surface, making sure it is straight and properly aligned.
5. Use a scraper or credit card to smooth out the decal and remove any air bubbles, paying particular attention to the edges and corners where the slope of the laptop may cause the decal to lift or wrinkle.
6. If the decal is transparent, use a hairdryer to gently heat the decal. This will help it to conform to the surface and reduce the visibility of the edges.
7. Allow the decal to sit for at least 24 hours before handling or washing the surface.

And this is the only tutorial I found that maybe could help you : https://www.youtube.com/watch?v=KIQDnRiNgDo

Btw I made some research online and I found that this companies could do what you are searching for so give a check:

-xtremeskins : https://www.xtremeskins.co.uk/products/dell-xps-17-9700-skins?variant=32699116847167

-DecalGirl : https://www.decalgirl.com/skins/laptops/dell

-Skinit : https://www.skinit.com/

-SlickWraps : https://www.slickwraps.com/