You will be able to edit all the textures that are in it in the next version (with the current text positions though!). For further updates you will be able to change the text positions as well! As you mentioned you already can fully customize where parking meter/ticket/nothing will be shown for basically every inch of the map.
What I could do is implement more parking permit textures for zones like Del Perro etc. That would not be too difficult, I'd just slap some basic textures on it and everyone can customize & upload for their needs. I'll put that on my todo list!
And to everyone, please be aware, I currently have my exams for university, so the next update might take another week or so 🙂