I wish to attach about 40 small mirrors around the outside of a disk.
The mirrors are 10mm square and the disk will be about 130mm diameter
and 10mm thick. The disk will spin at about 300rpm.

I need to be able to adjust the tilt of all the mirrors so that they
all point in slightly different directions. Can anyone think of a good
way of doing that?

The mirrors have a sticky back so would be stuck to something that
could be adjustable. That would have to be small and lighweight. Once
adjusted, I don't want the setting to change.

Now that I've typed all this I have thought of a very simple solution.
But maybe yours is better!