HL1 did get ported, and so all the textures you're doing have "their place" in the port. I see no reason why when it's released, someone couldn't take these images and replace the existing material images with them.
What's going to be the biggest issue is the rescaling of all these textures in the original map source. The port is done with all the original textures in their original scales. So you can't just toss in a 256x256 replacement for a 64x64 without modifying the original map source. Though their scale didn't change, they did get improved by adding reflective properties, etc.
FYI, as some of you (*cough*Zafod*cough*) may know, Source textures are now refered to as "Materials". Each one is in it's own pair of files, rather than being crammed into a "wad" file. The first file for a material stores the image (basically), and the second is a text file containing specs on the material. Stuff like it's material (wood, metal, etc.), what image to show in the editor, properties for water (like reflection, fog when viewed from out of the water, and when in, etc.), two materials you can use if you want to blend two of them together, and a lot of other stuff I shouldn't talk about :^)