The poem was written by a real sailor of long experience, not by some music-hall poseur or hack. He wasn't infallible, but he knew what he was about, and certainly knew "aboard ship" lingo better than we do. I see "hairy visage" as an arch little wink, an ironic juxtaposition rather than a poetic indulgence. IMO, it comes down to (1) is one's judgment better than the author's? and (2) does a change make the poem into a better song (with better scansion, clarity, sonal quality or color)?

The folk community often hears only one version of a song, so they seldom have the freedom of choice you ascribe (particularly when arrangement copyrights come into play). While a performer may have a free hand in adapting old works, the "anything I do is right" attitude does a disservice to both the original authors and audiences. Hearing a deficient adaptation of a work colors people's perception of the original work itself, and of its author. And once one version becomes established, whatever its relative worth, any variations from that de facto "authorized version" tend to be viewed heretically, not according to their own worth--even if reverting to the original wording (which the audience has likely never encountered). But this line of thought is getting rather far afield. Ultimately, each adapter makes his own decisions for his own reasons, and others have no opportunity to offer feedback until the damage is done, so to speak. Another reason to be circumspect.