[6.3] How can I change the bit depth of a whole bunch of castmembers at once?

Select all the castmembers you wish to change the depth of in the Cast Window. To make a discontinuous selection, hold down the command key (for the Mac) or the control key (for Windows) while clicking rather than the shift key.

When you've selected all the casts you want, choose "Transform Bitmap..." from the Cast Menu. The ensuing dialog box will allow you to alter the bit depth and palette of the entire selected set in one go.

Note: it doesn't matter if some non-bitmap castmembers are part of the selection. Text, sound, digital video or other non-bitmap castmembers will simply be excluded from the transformation.

[Thanks to Rich Martin (rmartin@tiac.net) for pointing this out.]