Hey Paul,
making your own custom cables, as described here, requires equipment like crimp pliers inserts and knowledge.
The tin-plated Molex connectors found on the Onefinity and Buildbotics Controllers are NOT made for frequent plugging.
What I imagine could help you would be a switch that can switch back and forth between the Y-motor and the rotary unit, and to which custom cables are connected. If you don’t have the equipment/knowledge on how to do this, I imagine there is someone waiting to make this custom thing for you everywhere in the world. You could search for a makerspace in your area and try to find someone.
Welcome to the forum!