There is a github repository here: https://github.com/companieshouse/api-enumerations
Officer Roles are in CONSTANTS.YML
I wouldn't expect them to change very often. Unfortunately there isn't anyway to track changes beyond keeping an eye on them and this forum.
I asked impementing some kind of feed or changelog, And they said they'd look into it and let us know, but that was in 2015 and I'm still waiting!