replacing zerks in old model aciera F4

Has anyone done this? I'd like to replace the zerks on my aciera with more modern ones made for a grease gun ---- unfortunately there's no flats on mine, so it looks like removing them may destroy the housing (they are really stuck on).

Does anyone know if these just unscrew? (And, what the threads are if they do so I can pre-order some zerks)?

Thanks!