Originally by @thecrazyscot, this will generate the *.Art.xml for your mod based on whatever *.artdef and *.xlp files are present.
The executable (exe) in this zip basically pulls through all artdefs and xlp files from your project and rebuilds your mod.art file for you with the elements in the right places. All you need to do is copy paste the directory in which your project's *.Art.xml file is located into the dialogue that pops up. The tool will create a backup for you and then rebuild. This process will need to be repeated each time a new artdef or xlp is added of course (so you might just want to wait until you've done all those bits)
thecrazyscot's Mod Art Generator v3
Updates *.Art.xml file based on *.artdef and *.xlp files present in mod.