I agree that the tempo change is unfair, but to my ear it is how the song is performed, I'm not sure how you'd realistically recommend fixing it other than something like pretending the note is a 78/128 note or something silly.

It won't prevent an experienced player from full comboing the chart, it is just a case where you have to be familiar with the song. It matches the music, and I don't really know of any reasonable alternative other than removing the notes entirely or doing something even more unexpected.

(Moreover, a tempo change right before the following monsters causes a sound glitch in the game—the attack sound and the hit sound on the monster will still play at the old tempo. This might get fixed later, but for now, it’s something to keep in mind. Again, I’ll refer to my Sick Of You chart, where in some sections I had to add 4–5 empty measures. If I had placed monsters there, their sounds would have glitched, confusing the player significantly.)

A very inventive chart. I can’t imagine how much effort it took to keep it in sync because, even by ear, the tempo fluctuations are noticeable—the recording clearly wasn’t made to a metronome. Personally, I avoid working with such tracks since the tedious task of adjusting BPM down to tenths and hundredths is too exhausting.

The only downside is the sudden tempo change for one measure at the very end. It happens without warning. After working on Sick Of You, where I had a lot of tempo changes, I made it a rule to always adjust the tempo in a way that gives the player time to react—meaning, I leave a few empty measures after the shift.

Honestly once you learn how to beat the Super Meat Boy tracks in hard you start being ready for the impossible shenanigans.
I would even go as far as to say for an impossible track yours is quite forgiving : plenty of food and some room to breath
Not that it's a problem

Congratulations, the Impossible chart has some really weird rhythms and tough tricks! I'm impressed you were able to clear it.

Amazing work
I was sleeping a little bit on Hard
But then I tried the Impossible and, damn, it's pretty saucy lol
I got a C... like Cowboy Bebop!