You do get an audit log event that an access control policy has been changed (and by whom) as well as an audit event for the deployment. I just verified this on an FMC with the current 6.2.0.1 software.
You do not see the details of what the changed rules are in the audit event. I don't know of an easy way to see those changes retrospectively.
If any of the component policies (Intrusion, File etc.) are changed, you can compare them, includng revisions of a given policy.
Reference:
http://www.cisco.com/c/en/us/td/docs/security/firepower/60/configuration/guide/fpmc-config-guide-v60/Policy_Management.html#task_ABA1FE48DBBB44BC9FF40243FCC58BF6