Perhaps it is obvious, perhaps not...
If you want recenter a ceiling grid in a room, assuming that it has been adjusted already but you need to change it again. Add a dimension string to the defining boundary walls and to one of the parallel grid lines, click the EQ control toggle. The grid repositions itself.
If you have a specific corridor width (say 6'-0") that a 2x2 or 2x4 ceiling should fit nicely in but it isn't in the correct spot, same trick but add a second reference to the other side of the same ceiling "panel" and use the EQ control toggle.