In design mode, you can edit the name of a mode in a text box and click "Rename Mode". Would be simpler to just rename the mode as you type changes.
(Ideally would replace the mode title in the title bar with a text field so you could edit in place.)
Type the name, press enter.
This is not obvious, since the focused component is not in a dialog.
Why not simply rename as you type?
OK. Instant rename seems more user friendly.
Integrated into 'main-golden', will be available in build *201108280601* on http://bits.netbeans.org/dev/nightly/ (upload may still be in progress)
User: Jaroslav Tulach <firstname.lastname@example.org>
Log: #201362: Instant mode rename while typing