Thanks both!
Indeed, right-click hold then shift does rotate the selected atoms. I hadn't appreciated that pressing shift before or after the click led to different outcomes. Thank you - problem solved.
On the other strategy...
I just tried again and doing
ui mousemode shift right "rotate selected atoms"
does not work as I expect, in that if I hold shift first, then right click and drag, the selected atoms are shifted, not rotated.
If I right click and then press shift, I do get rotation, as expected based on what I learned today.
Tom - I don't know what the difference could be between what you are doing and what I'm doing. Are you definitely pressing the shift key before right-clicking? Just to give more info, here's the output of mousemode:
control left: select
control,shift left: select add
control,alt left: select subtract
left: rotate
middle: translate
control middle: mode name
alt right: rotate selected atoms
right: translate selected atoms
shift right: rotate selected atoms
wheel: zoom
shift wheel: mode name
control wheel: mode name
alt wheel: mode name
pause: identify object
Available modes: select, select add, select subtract, select toggle, rotate, rotate and select, rotate selected models, rotate z selected models, rotate selected atoms, rotate independent, translate, translate selected models, translate xy selected models, move picked models, translate selected atoms, zoom, clip, clip rotate, identify object, pivot, swipe as scroll, none, zone, pick blobs, swapaa, play coordinates, next docked, contour level, move planes, crop volume, windowing, rotate slab, label, move label, distance, bond rotation, tape measure, tug, minimize, play map series, mark maximum, mark plane, mark surface, mark center, mark point, link markers, move markers, resize markers, delete markers, map eraser, isolde tug atom, isolde tug residue, isolde tug selection