Here in the printer’s manuscript, the subject pronoun I was inserted in pencil. The I is written quite lightly and rather awkwardly, as is also the insert mark. This I seems to have been inserted in the printer’s shop by either John Gilbert (the 1830 compositor) or Oliver Cowdery. Penciled corrections in 𝓟 seem to have originated in the printer’s shop (for additional discussion regarding secondary editing in pencil, see under Mosiah 11:23). Irrespective of who made the emendation in 𝓟, it does appear that this change was made without reference to the original manuscript. It is quite possible that the original manuscript had an I that was accidentally deleted while copying from 𝓞 into 𝓟.
The first question to ask here is whether the Book of Mormon text has other examples of yea and followed by a complete predicate but without restating the original subject. In fact, there are quite a few examples, and for each example there is always tense or modal agreement between the conjoined predicates:
Moreover, in all these examples the clause following the yea and seems to work perfectly well without the subject. There is no difficulty in processing the sentence or in recovering the subject.
On the other hand, the example from Mosiah 17:10 seems particularly difficult to process— and for a couple of reasons. First, the preceding clause is in the present perfect (“I have suffered myself that I have fallen into your hands”), while the conjoined predicate has the modal verb will (“yea and will suffer even unto death”). Second, the conjoined predicate “will suffer even unto death” does not really relate to “I have suffered myself that I …” . It seems quite impossible for the intended reading to be “I have suffered myself that I … will suffer even unto death”. The clash in tense and aspect seems wholly unacceptable. Instead, Abinadi’s statement that he will suffer even unto death appears to be related to the earlier statement “and that ye may know of their surety”—that is, the intended reading is “and that ye may know of their surety ...I will suffer even unto death”. The insertion of the subject pronoun I guarantees this reading. All the cases of yea and listed above are conjoined with the immediately preceding predicate and agree in tense and aspect. Thus it seems quite reasonable to assume that the omitted I in the earliest extant text for Mosiah 17:10 was the result of an early error in the transmission of the Book of Mormon text. It hardly seems possible that the I would have been intentionally omitted in the original text.
There is evidence that the scribes would sometimes accidentally omit the subject pronoun I when conjoining predicates, as in the following examples:
The first of these is particularly relevant since the I was apparently lost after yea and; for discussion, see under 1 Nephi 5:8. As here in Mosiah 17:10, the yea and in 1 Nephi 5:8 is not related to the immediately preceding clause (“the Lord hath commanded my husband to flee into the wilderness”) but to the clause before that one (“now I know of a surety that …”).
Summary: Accept in Mosiah 17:10 the correction in 𝓟 that added the subject pronoun I (“yea and I will suffer even unto death”); a similar emendation in 1 Nephi 5:8 is consistent with the addition of the I here in Mosiah 17:10.