Hi Jane,
Sure, please see '3drefit -help'.
That program does not alter the BRIK contents at all, it
only alters the HEAD file. Options such as '-xorigin'
depend on the orientation of your dataset. If it is in
ASL orientation, then x is AP, y is SL, z is LR. And an
option like '-xorigin 123.4' will set the new x origin to
123.4mm Anterior.
You might save a copy of your original before playing
around. The 3drefit command is destructive, i.e. it
actually modifies your file, without creating a new one.
- rick