Question Merging 2 projects or try something else

I want to add an object highlight on selection. I've tried using one of the most common solutions - change material, but it doesn't work in my case (I have many object with 3 materials assigned to each of them).

Now I want to try a different approach - using render highlight. As far as I've figured out, a new Unity project template has to be used (Universal Render Pipeline). Thus, the current template I am using (3D) is not suitable and a new project has to be created.

So, I was wondering, what is the preferrable solution for this case: should I create another separate project with URP template and then merge these projects (btw, I have tried and failed to do so) or is there a possibility to edit render in 3D template project?

Thanks in advance