Maybe they had started recording other tracks along with the MP3 already ..

I wasn't questioning 'why' the OP wanted to do this, just trying to suggest a possible 'how' smile

In the example below I pretty much needed to do the same thing
All the other tracks were already done and part of a pre-existing project, but suddenly they needed new drums.
Selecting a 159/160 tempo and just generating drums would never have worked, it needed to line up pretty exact to the expected beat (and it waivers a bit) plus have fills where expected/desired
ACW to the rescue!
To me this 'generated' drum track has just as much feel as any other drum track on this particular CD
I would never have been able to do this without the ACW and RB editing

https://flythewreckage.com/wp-content/uploads/2020/06/09-Track-9.mp3

/hey the drums worked

I do not work here, but the benefits are still awesome
Make your sound your own!