That's the thing, they aren't changing the mode of operation. To sum up, basically the rules say you cannot change the mode the gun shoots in (semi, ramp, auto, etc.), and you cannot change air pressure settings (increase/decrease velocity). I have not come across anything that says you cannot change the flight pattern of a paintball.
And here is something to consider: Tippmann flatlines would be completely legal. There is no rule that I know of that excludes the flatline. As for the apex, the thing that would make it illegal (if it is) is the adjustability of it. Adjusting it will not change the mode of operation (i.e., semi to ramp) and it will not change the velocity, so it cannot be excluded on those rules.
Now it IS legal to adjust eyes (on/off) and loader (speed setting, on/off, etc.) So be adjustable alone does not make it illegal.