Because Lume CMS is proxying a single github user when it git commits, there's no tracking of what user made what change.
If a "save comment" field could be added to the UI, users could enter something there depending on whatever workflow they want, and the CMS could copy that into the commit message like:
Changes from CMS
RC: added paragraph on the blah blah topic...

I hope you might consider this or some similar solution to let teams track what each person did, somehow.