The Mac system caches all preferences files in RAM. Changing them on disk has no effect, so deleting the preferences file will do nothing, the Mac system will rewrite it from RAM. If you want to reset all your preferences to their original (shipped) state (except for the Nisus New File which has its own button in the New File preferences, you must use the Terminal.

1. Quit Nisus Writer Express.

2. Launch the Terminal.

3. Paste the following command:

defaults delete com.nisus.NisusWriter

4. Press ⏎.

5. Restart Nisus Writer Express.