Batch file for joining audio files (FFmpeg) in random order

[kolamorx]

I have this batch file, which does the job:
@echo off
setlocal EnableDelayedExpansion
for %%i in (*.wav) do (
ren "%%i" "!RANDOM!_%%i"
)
endlocal
(for %%i in (*.wav) do @echo file '%%i') > mylist.txt
ffmpeg -f concat -i mylist.txt -c copy out.wav
However, I want to limit the random numbers to 100-999 and to remove the first 4 digits (3 numbers and _) after the joining process is over. In other words, to rename the files names back to their original names. (I don't think there is an option to just undo renaming.)
Does anybody know how to do this?

[stax76]

With powershell it's relative simple.

dir *.wav | sort {get-random} | foreach { "file '$($_.Name)'" } | out-file -en default list.txt
.\ffmpeg.exe -f concat -i list.txt -y -c:a copy out.wav