Yes, this is actually very possible! You can actually replace any terrain texture with any other texture. In a risk-style map I made, I replaced the "abyss" (no walk/build) tile with a rock texture, so I could use it as cooler looking mountains/cliffs.
You can do this with blight too
If you don't already have the Warcraft3ModelEditor, download it here
War3 Model Editor - The Hive Workshop - A Warcraft III Modding Site. (it's awesome anyway, not just for this)
I'm using this mostly for its mpq browser, so if it doesn't work, you can find another browser (theres more on the page). Remember, when you start the program it will have an empty gray window, that's whats supposed to happen.
1) Start up the program (WC3ModelEditor), then go to Windows->MPQ Browser.
2) Click File->War3.mpq
3) Wait for the mpq to load, then go down and open the "TerrainArt" folder
4) Find the texture you want to use as blight. I'll use the cityscape tiles (TerrainArt\Cityscape\City_BrickTiles.blp) for example (You can double click any texture in the mpq browser to view it in the main window)
5) right click the texture you want to use, and pick "extract"
6) Rename the file to the name of the texture you're replacing. To look at the names of the blight textures, open the "TerrainArt\Blight" folder, and find your blight texture (the default is "Lords_Blight.blp" for the "Lordaeron Spring" tileset)
7) Import your tile to a warcraft3 map with the import manager
8) Double-click your imported file in the list and change the "Warcraft3Imported\" path to "TerrainArt\Blight\" (ex: "TerrainArt\Blight\Lords_Blight.blp")
This will replace the blight tile texture with the cityscape tile texture.
I'll attach a map with an overridden blight texture as well...
That was probably a little too-in depth, but it'll get the job done