An Ashkenazi Who Prays in a Nusach Sefard Minyan

Hello and blessings, Rabbi. I pray according to Nusach Ashkenaz, but on Rosh Hashanah I will pray with a Hasidic minyan that has the custom to blow the shofar in the middle of the Shemoneh Esrei prayer and then to recite “Hayom harat olam.” How should I conduct myself: should I recite it with them, continue the rest of the prayer according to my custom, pray the entire Shemoneh Esrei in Nusach Sefard, or not recite it at all?

Peace and blessings 

Listen to the shofar blasts quietly in the middle of Shemoneh Esrei, and do not recite any piyyut. 

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