Hi Eemshoorn,
You can convert a static ship, or an AI ship, to a player ship, but you can’t control her unless she was originally made as a player ship—with a bridge and controls. Not all ships in SSE have player versions.
If you start with a player ship, and board her, she can then be converted to an AI ship. You can ride her as a passenger, and visit the bridge, but you cannot control her until she converts back to a player ship.
In one of the Autopilot topics I posted an example mission that does that.
Regards,
Marty