🚀 go-pugleaf

InDesign can (kind of) do it in the UI. What you have to do is, every time you want the header to change, start a new section (by, for example, right clicking on the page in the pages palette and choosing "Numbering and Section Options") and enter your desired header text as the "Section Marker". Then, in your master page, insert the "Section Marker" special character where you want the text to show up.

This can, of course, be scripted. Scripting will also let you vary more than one thing at a time (but not by using Section Markers�you only get the one). It's certainly no replacement for frame's variables, but that's all you get out of the box. There are doubtless any number of fine plug-ins that people will be happy to sell you as well.