A TL member on either profile can change an LNAB.
But you shouldn't change one to match the other before merging. That just creates an extra redirection to no purpose.
On the other hand, if a 3rd LNAB is preferred choice, one of them should be changed before merging. Only a TL member can do this.
But then, if they can't complete the merge immediately, they lose control, and we still have two different LNABs sitting there. There's now a good chance that the merge will be done the wrong way, and in the meantime, there's still a good chance that somebody will block the merge because of the LNAB mismatch and we're back to square one.
And if it gets as far as default approval, it still needs a TL member to change an LNAB before a merge.
One of the PMs has already blocked the merging of the wives.
Who'd think WikiTree has been around over 10 years. It's not like variant spellings in the sources are an isolated or unusual issue.