Switching Omer periods of mourning

Hi,

I observed the "first days" of the Omer last year, refraining from a haircut until after Lag ba'Omer. May I switch to the "second days" this year, observing from Rosh Chodesh until the end of the Omer?

Rav Moshe Feinstein ruled that one may switch from one set of 33 days to the other from one year to the next. There are only two caveats:
• One must observe one set of 33 days in entirety; one may not take a haircut before Rosh Chodesh, and again after Lag ba'Omer.
• One may not veer from communal minhag; if a community has a defined practice of observing a specific "half" of the omer, one may not vary from that practice.

(Shulchan Aruch Orach Chaim 493:3; Chatam Sofer Orach Chaim 142; Mishneh Berurah 493:17; Igrot Moshe Orach Chaim 1:159)

Have a great day,
Mordechai