You just want to position the component by an offset value from the initial XYZ dataum planes? That is possible but loses the value of the assembly constraint routines. Alot would depend on how complex your assembly is, too. I would not want to do that for a car or an aircraft, but a mold might be doable.
You can also create additional datum planes in relation to the initial ones to mate your components against. This may work better if you have a component at an angle from the main datums.
I found it best to position my initial component to the datum planes then mate additional components to either surfaces on a prior component or additional datum planes.
"Wildfires are dangerous, hard to control, and economically catastrophic."
Ben Loosli