Hello and welcome to the site...you will just love it and gain so much knowledge.
Someone else will have to help you with the L&P as an overlay on nail art I assume you mean after blending tip and putting a layer of overlay on & then the nailart with more overlay or do U mean onto a natural nail with overlay after? sorry if I am confusing you.

If you have not blended the tips first and taylored them to your own nails I don't think you could now apply them to your nails without ruining the design due to blending....
Anyway I seal my nail art with either a good top coat or a couple of layers of brush on resin (used in fibreglass systems).
I am sure you know that you can do nail art on top of the overlays and seal with a good top coat and apply another layer the following day then once a week and I have found this these can last upto 3 weeks. Hope this is of some use to you..
Hope to see more posts from you soon....All the best...