Had that been the case (it was not), a request to Avid to extend that capability to a user definable XY location for tool changes for "normal" 3 axis work might have been easy. I don't speak for Avid, but that request would seem to be a reasonable one to my way of thinking.

The touch plate and ( I am still waiting for mine) , is designed to set the work piece x-y corner and work piece Z zero. As I understand the final setting of the work piece Z zero after the touch off, is dependent on the distance you enter in the set up. So you could use those zero points for your manual tool change. Or you can use the Home for the machine location for your tool change point.