The modifications make the code more complicated, and as originally suggested, it doubles the RAM used for each servo.
The servo direction can be reversed without adding code to the library by using the map function in a sketch ( or something like servo.write( 180-pos)
Trim can be changed using the optional parameters that set min and max values to attach.
Vinceherman's modification to change trim is more convenient for him in his application but it may seem odd to some people to have a trim function that results in a command to send a 1500us pulse actually produce a pulse that is not 1500us.
A nice thing about having source code available is that it enables people to customize things to suit their needs. But making code bigger and more complicated by adding features that most people won't use is usually not a good thing to do.
That said, I am all for vinceherman posting his modifcations in a thread for people that want these features.