How to skip already imported textures on AssetPostprocessor change?

Once in a while, I want to adapt my AssetPostprocessor for textures, so it automates the process of importing textures in new folders. I use the GetVersion method and increase the version by one when I'm done.
The problem is, whenever I do this, everything get's reimported. Even though 99% of the textures already in the project are not going to change at all, because they've been imported once.

Is it possible to skip already imported textures? Maybe a solution by which I can tell the TextureImporter for each texture if it should be reimported or not. Like an else case where I just say skip. Once the script fully ran I would not increase the version number once more and just remove that code.

Is something like that possible? Running the importer only on new files?