I assume you mean manage your devices with TACACS (NCM doesn't use TACACS). Within NCM, you can only assign one profile to a device so if NCM wants to back up a config, then it will always use the same device. If you have RTCD turned on, then any TACACS user can modify the configuration of the device. Once they exit conf t mode, syslog will trigger an exe to will backup the current configuration.
In syslog when someone changes a configuration on a device, it usually shows up as "Configured from console by username on vty0 (x.x.x.x)"
I hope that help as I'm not 100% sure on what you were exactly asking for.