I am sorry, but the more we argue, the more I get the feeling, you don't know what you are talking about.
Last try on a basic level:
Prefab vs. normal Track
Right now we have on any coaster two kind of tracks: The normal track: straight coaster track, you can bend it to a certain degree in all 3 dimensions, you can give it an incline, a banking angle and even a predefined length. This is track that needs to be placed manually by the player. In 'edit' mode you can make modify the track in all 3 directions to a certain degree.
Then we have prefabs basically everything you can place in 'construction' mode. Most of those prefabs you just can modify in length and only in length. , i.e. brakeruns, coaster elements (when you make a loop bigger, you make the track longer not the incline of the actual piece.). Some elements like lifthills, drive tires, etc you can rarely bend in two directions. These elements are not smoothable and are very limited in what you actually can do with them. My educated guess is these limitations are somewhat hardcoded (means they are implemented in the game engine not in the game itself).
Smoothing
What does smoothing do? With smoothing the Gameai tries to make the selected coaster track into a straight track, as much as it can. This results that all edges are get smooth out. To smooth a track the game needs to modify especially the incline and banking of track, to some degree the length too.
Your Idea
First of you want to split the loop into diffrent pieces, I highly doubt that this possible accounting to the known limitations, this is why my first idea was to have like 10 looppieces you have to place by hand, but even it is possible, this would still mean they would be prefab-pieces (and not magically , to some degree you could adjust the size of each single piece, like you can now with the whole loop even after construction, but you can't use the smooth button, it will be greyed out. So you rarely could achieve a smoother loop by manualy adjusting the height of each single piece. Since it is prefab, this would be very tedious and you need to wiggle some room out of it. (make the top a bit larger to give you some on the entry, and keep in mind you need to adjust the exit too afterwards and so on). This would be more tedious and time consuming than just 'draw a custom loop' and smooth it afterwards.
I am just wild guessing here, since i don't know exactly your issue (transition in and out is rather vague) but you can try to mitigate the smoothness if you place a 4m straight track piece before the loop, resulting that you can smooth out your track before hitting the transition.