The short answer is "no". The approach speed is probably hard coded into the program, not the individual station assets. When Trainz 2010 first came out there were users who reported a problem with trains overshooting or completely ignoring AJS stations because of a speed issue - I believe this was caused by a change in the physics (braking distances, etc) that Trainz 2010 introduced.
The longer answer is "yes" but it is a lot of trouble to achieve. It is possible to "adjust" the physical behaviour of locomotives by altering brake pressure, maximum speeds, etc using CM but the changes are notoriously fiddly, would require a detailed knowledge of train physics and everyone who downloaded your subway layout with the higher speed approaches would have to make the same manual adjustments to their locomotives.
Peter Ware