VoxCommando doesn't create this file, it is written by the voxtools add-on in XBMC, so only XBMC should require permissions. I don't understand your file setup or why each client does not use its own directories, but this sounds more like a "file being accessed by multiple programs " problem rather than a permissions problem. I don't think XBMC clients are intended to share these folders but you coul try asking an XBMC expert.