Definitely possible, but probably not easily. The "easiest" remastering I've seen simply upscales textures to 2K or 4K which provides an inexpensive way to resharpen old games without losing too much of their original look.

For this HL2 RTX mod though, my understanding is they had to add all new lighting sources to hopefully match the original intent, and looks like they remodeled many items and actors too.