Yes; doesn't matter if it's your first, second or final extension. It will all get auto-extended to April 30 first, and then later we'll hear what's up after that.
Chiang Mai office clarified that they apply it to any kind of visa or extension of stay. All automatically extended to 30 April, without charge and without the need to visit.
What kind of visa do you have? For tourist visa and visa-exemption you don't need to do anything. If it's a non-immigrant visa (extension based on marriage, employment, education, retirement, etc.) then I would call and ask.