Scribe 2 of 𝓟 initially wrote “baptized into repentance”, but then he immediately corrected the preposition into to unto by overwriting the i with a u (there was no change in the level of ink flow, nor was there any dot for the i ). Undoubtedly, the original manuscript read unto. Elsewhere the text refers to “baptizing unto repentance” (12 times) or to “baptism unto repentance” (once, in Moroni 8:11). The use of unto follows the King James language in Matthew 3:11: “I indeed baptize you with water unto repentance”.
Scribe 2 of 𝓟 frequently mixed up unto and into, at least initially as he copied from 𝓞 into 𝓟; in the following, I give the actual reading in 𝓟:
Except for the second example in Mosiah 26:27, scribe 2 initially wrote into in place of the correct unto (as here in Mosiah 26:22).
Summary: Retain in Mosiah 26:22 the use of the preposition unto in “baptized unto repentance” (the corrected reading in 𝓟).