Hi Eben!
Yes, your keyword is ‘Layout Adjustment’ (at least that’s what it’s called in ID CS2).
The InDesign Help is pretty expedient on this.

Furthermore, the basics of this function are explained in ‘InDesignSecrets Podcast Podcast 053’ (Transcript – quite to the end of the episode).
F

The text box change will only occur if you have used Master textbox in creating the document and have not moved it individually on a single page.

ChrisL

Have you tested that, Chris? I’m pretty sure that this isn’t 100% true. IIRC, you can make use of Layout Adjustment even if you didn’t check ‘Master textbox’ when creating the document. You need a Master Sheet with guides – or margins, of course.

If you have master text frames on your Master page and adjust them, the corresponding frames on the document pages will change accordingly, as long as you have not manually adjusted the text frame on a document page, thereby breaking the Master's control over it.

If you're talking about individual text frames on document pages (not created via or governed by any master text frames), then Florian's tip about Layout Adjustment is the way to go. Read up on it in the Help: it's not a magic bullet. But it is intended to do the sort of thing that I think you're asking about, as long as your initial conditions are right.

-- K.

Kent has explained my meaning better than I did :-)
Thanks Kent!

ChrisL