In the printer’s manuscript, Oliver Cowdery initially wrote the conjunction for at the end of the line; then virtually immediately he crossed it out and supralinearly inserted but near the end of the line (there is no change in the level of ink flow for the correction). The connector but obviously works much better since the following sentence contrasts with Mormon’s initial desire that all might be saved. The but was probably the reading of the original manuscript since the correction appears to be virtually immediate.
Summary: Accept in Helaman 12:25 Oliver Cowdery’s correction in 𝓟 of for to but, the probable reading of 𝓞; the for does not really make sense here.