It would help if you were a bit more specific as to what you were configuring while on the ground, but I will try and describe what happens and why. I am assuming you are using the EXPERT mode in SkyView, not SIMPLIFIED.
1) You can pre-set the altitude and heading you want before takeoff. These will not change at any time.
2) You cannot pre-set VS or IAS mode. These always synchronize when you engage. We don't allow you to set these beforehand since you will get huge jerks up or down if they are not dead on when you engage. This is pretty much the way all autopilots work. Once engaged, you can use NOSE UP/DN to adjust your target.
3) If you turn the Flight Director (FD) on when you are on the ground, it will turn off as you start your take-off roll. For a FD to be useful in a take-off requires a lot of set up and knowledge about the plane, because it needs to guide you through a safe departure. We don't want someone following this in this situation since we can't do it perfectly.