How can I change the top layer extrusion width?
Is this only possible via extra processes? IF I do have a part with 50 different top layer hights I have to do 50 processes or is there any workarround with skripts?
There are several settings for the top layer on the Infill tab. You would typically adjust the "top layer extrusion modifier" if you need slightly more or less plastic on the top layers.
Note that "top layers" refers to any surface that is visible from the top of the part, not just the very last few layers of the entire print, so it will automatically be applied to the entire model without any other effort.
I don't think you can typically change the extrusion width for the top layers alone, since it uses the same width as the perimeters by default. You might want to look at the ironing features, since they might help you get some of the top level surface finish you are looking for.
The brute force way of doing this is to use the Multiple Settings Wizard and define the transition plane to be exactly between the top two layers. It would require some computation outside of S3D based on initial layer height and other layer height to figure out what that Z position is.