I guess it's okay if the singer makes up some of his own lyrics, too?
And what about that intro guitar lick? Is that an important part to keep or can the guitar player just wing it?
Well, yeah, it's not a Schubert lied either.
Have you ever heard of "floating lyrics"? Those are the ones that end up getting found in multiple songs because they're just out there in the consciousness. One classic example: "If you see me coming, heist your window high... [repeat] if you see me going, hang your head and cry") Have you ever listened to anything recorded by the Carter Family, or Jimmie Rodgers? Have you ever noticed that some of the words don't seem to make sense? That's because they needed something to go in a spot and they did something. "Twine with my mingles"?? Really? I'm sure originally it was "twine with my ringlets" but somehow Sara Carter got "mingles" in there, and it's still there almost a hundred years later. Somewhere along the way "Can the circle be unbroken" got changed to "will the circle..." No one pitched a fit.
Moving a little closer to the current day, how many people do you think have played and/or recorded "I'm so Lonesome I Could Cry"? Do you REALLY think that every one that didn't play and sing it exactly like Ol' Hank did, was doing it "WRONG! WRONG! WRONG!" ??
I often sing a song by the Delmore Brothers called "Fast Express". I've written a couple extra verses, humorous in intent, to give a little more space for instrumental solos between verses. Are the Delmores going to call down the wrath of Jehovah on me from their seats in heaven? Do I need to be worried about lightning bolts?
Come off it. What you've got there is a song - as someone pointed out, if we're talking about Stapleton's version, he's already changed the basic song from from the most well-known version (Jones') - that is a very simple chord progression, played quite slowly in 12/8. I would frankly be astonished if the bass player on that recording needed more than two times through the thing to nail it. Any professional studio bass player would walk in, hear "we're playing "Tennessee Whiskey" but I'm going to do it as a I-minII-minII-I - liike that Etta James song" and the key, and would play the part you hear on the recording. There were not written charts. The bass player made that up out of his head. Basically, if you want to play a Chris Stapleton type Tennessee Whiskey, you play very simply in 12/8, and you're done.
I'm willing to bet that the preparation for recording that song, the recorded version of which you want to enshrine as the one true way to play it, consisted AT MAX of Stapleton banging out the chords one time on the guitar so everyone knows how he wants it to go, and MAYBE having a piece of paper with all the lyrics in front of him just in case he blanks on a line.
For the vast majority of popular music, there IS NO ONE TRUE VERSION. Not understanding this is why people get all wrapped round the axle when singers want the tune in a key they didn't learn the one true bass line in.