From: Rabbi Moshe Sofer
To: Rabbi Yehoshua Katz
A Kohen who already performed nesias kapayim in one minyan asks whether he must recite the bracha again when blessing a second congregation during the same prayer. The Chasam Sofer distinguishes four scenarios: different prayers always require a new bracha, repetition within the same congregation is prohibited, and with a different congregation it depends on whether other Kohanim are present—ascending with a bracha only when no other Kohanim are available.
Source: Shu"t Chasam Sofer OC §22