The 1908 RLDS edition removed the relative pronoun which here in Ether 14:24, which made the last clause an independent clause. Joseph Smith, in his editing for the 1837 edition, crossed out the which in the printer’s manuscript, but the 1837 edition itself did not implement this emendation. In accord with the corrected reading in 𝓟, the 1908 RLDS edition adopted Joseph’s editing here in Ether 14:24.
The motivation for dropping the which may have been that it didn’t seem right to use the verb avenge to refer to avenging oneself “upon the word of the Lord”. In modern English, we do not expect such usage. In a note at the end of the verb avenge, the Oxford English Dictionary points out that avenge occasionally has meanings that do not refer to retribution; that is, avenge can be used in broader contexts where the corresponding verb revenge would not be appropriate. The OED, for instance, cites examples like these under avenge:
These more general applications of the verb avenge imply that one can also avenge oneself “upon the word of the Lord”.
It should be noted here that the independent clause in the current RLDS reading (“and the word of the Lord came to Ether …”) implies that this is the first time that Ether has prophesied that Coriantumr would not fall by the sword. This is clearly not the case; this prophecy was declared earlier in Ether 13:20–21. Thus the use of the relative pronoun which in Ether 14:24 is definitely correct and will be retained in the critical text.
Summary: Maintain in Ether 14:24 the relative pronoun which in “and the word of the Lord which came to Ether that Coriantumr should not fall by the sword”; unlike the verb revenge, the verb avenge can take a prepositional phrase like “upon the word of the Lord” as its complement.