Actually, try using the Pk3ds tool to unpack and repack garcs.
This site builds the latest Pk3ds/Pkhex straight from the github.
http://teamcity.skyeditor.org/
1. login as guest,
2.select pk3ds
3.Click the dropdown on artifacts and download the zip file.
To get to the garc unpack/repack
1. open pk3ds
2. go to tools
3.Misc tools
4. (un)pack +BCLIM
4.1 unpack by dragging the garc to the block under decompress
4.2 repack by dragging the folder to the block on the right next to the repack drop down menu
5.rename and replace the old garc with the one that you just created.
Note- the new file will have a .garc extension ensure that you delete this extension.
6.profit