Modifying .vol files with a filter
If you need to make manual changes to a .vol file it is recommended to make these through the client interface ('gluster foo'). Making changes directly to .vol files is discouraged, because it cannot be predicted when a .vol file will be reset on disk, for example with a 'gluster set foo' command. The command line interface was never designed to read the .vol files, but rather to keep state and rebuild them (from '/var/lib/glusterd/vols/\$vol/info'). There is, however, another way to do this.
You can create a shell script in the directory '/usr/lib*/glusterfs/\$VERSION/filter'. All scripts located there will be executed every time the .vol files are written back to disk. The first and only argument passed to all script located there is the name of the .vol file.
So you could create a script there that looks like this:
#!/bin/sh`\ sed -i 'some-sed-magic' "$1"
Which will run the script, which in turn will run the sed command on the .vol file (passed as \$1).
Importantly, the script needs to be set as executable (eg via chmod), else it won't be run.