Supposing you have mylib.aar in your current directory, try the following:
$ unzip myLib.aar -d tempFolder # or other extracting tool
# Change whatever you need
$ jar cvf myNewLib.aar -C tempFolder/ .
Supposing you have mylib.aar in your current directory, try the following:
$ unzip myLib.aar -d tempFolder # or other extracting tool
# Change whatever you need
$ jar cvf myNewLib.aar -C tempFolder/ .