"Res" means thing. The res with respect to a trust would simply refer to that which is being held in trust also known as the trust corpus or the trust estate. The term usufruct is nifty but Boris hasn't seemed to arrive at realization that a military in occupation is not the sovereign. A resident is not necessarily the beneficiary. There is a term called remainderman.
Furthermore, the right of using and abusing neither vests in state officers nor in the occupying military. One of the ancient functions military is to dispense civil government until lawful government can be restore. However, even a military has a source of authority.