Here the 1920 LDS edition edited the connective or to nor. Such editing is not required since either reading is possible in standard English. Note, in particular, the following similar instances of “not ... or” elsewhere in the text, instances that have never been edited to “not ... nor”; in each case, the or conjoins two phrases that are both within the scope of negation of the earlier not:
In Alma 26:11, two prepositional phrases are conjoined by the or and are both within the scope of negation of the not: “I do not boast in my own strength or in my own wisdom”. The critical text will restore the original or here.
With regard to this change, Merriam Webster’s Dictionary of English Usage notes (under the second item listed for nor) that “nor frequently replaces or in negative statements”, which implies that from a prescriptive point of view the 1920 editing is optional, not required. For further discussion of the editing of or to nor in the Book of Mormon text, see under Mosiah 2:12–13. For an overall discussion, see under negation in volume 3.
Summary: Restore in Alma 26:11 the original or (“I do not boast in my own strength or in my own wisdom”); there is nothing grammatically inappropriate about the original text for this construction.