Sorry if this is a lot simpler than it seems to me, but I just can't figure out how to place an ucs on a part, with identical orientation as the containing assembly. I have placed a grunded workpoint in the part, on the assembly origin, but When it asks for a point to give the direction of X and Y, I am unable to select anything as I am in part edit. the only things I seem to be able to select are vectors on the solid. But those cannot be used, since the angles are different from the assembly's.
Please be aware the USC (User Coordinate System) command in Inventor is for a feature (part or assembly) and not the whole component or assembly. The whole part and or assembly will follow the WCS (World Coordinate System) which can’t me moved. If you still want to create one then you may need to create work points to orientate the USC to how you want it. If you want to just orientate the part that would be done using your assembly constraints. If the components need to follow the same WCS in the assembly and each component/part you will need to create the parts within the assembly and selecting the coordinate system you want to use as a common thread. Or you can create the component independently but again using the same coordinate system for the parts orientation this will require a little forward thinking.
In your description you mentioned Adaptivity can I ask how adaptivity played in to your UCS request?
In addition to the work points mentioned, you could fudge a UCS out of three planes and makes those adjust parametrically with the part your attaching to.