I’m so glad to hear that it’s been useful to you!
Updating this for Downie 4 should be fairly easy.
Just look for this:
elif [[ -d '/Applications/Downie 3.app' ]]
then
APPNAME='Downie 3'
else
and change it to this:
elif [[ -d '/Applications/Downie 4.app' ]]
then
APPNAME='Downie 4'
else
and that should be all you need to do.
If that doesn’t work, let me know and I can post a new script. (I can’t edit the original post anymore.)