When I type out a complex replace regex, there is often an error. I often need to be able to apply and undo several times before I'm satisfied.
At present (Geany 1.33), one must escape from the replace dialog, undo (which only applies to the current document, per https://github.com/geany/geany/issues/1631), and re-enter the replace dialog. This is poor workflow for a common sequence.