Here the 1907 LDS vest-pocket edition replaced the subjunctive were with the indicative was. This edition was not used as a copy-text for any subsequent LDS edition; thus the subjunctive were has been maintained in the LDS text. Elsewhere in the earliest text, there are 78 occurrences of “save it were”. For one of the 78 cases (in Mosiah 6:2), the current text reads “except it were”, but the original text read “save it were”.
Two occurrences of original “save it were” have been changed to “save it was”, probably accidentally since all the other examples of “save it were” have been left unchanged:
There is one instance of a momentary scribal slip that shows the tendency to replace “save it were” with “save it was”:
Here Oliver Cowdery corrected his initial error in 𝓟.
The earliest text has three occurrences of “save it was”, one of which is extant in the original manuscript:
These three earliest examples of “save it was” will be retained in the critical text, even though they may be errors for “save it were”. The natural tendency in the history of the text has been to occasionally replace the subjunctive were with the indicative was. For additional examples of the subjunctive in the Book of Mormon, see under mood in volume 3.
Summary: Maintain “save it was” only when it is supported by the earliest textual sources; usually the earliest text reads “save it were”, as here in 1 Nephi 17:31.