I've logged this as a bug, I should be able to have it only export custom fields from selected forms in the next update.
The form log "message" field is the data captured at the time of submission. It won't reflect field changes like that. The csv export will still export the latest data.
No edit log support is not supported. It's theoretically possible and something I can look at in the future but this app is mainly focused on contact/form submission and wasn't thought of as a database like that.