Can I decrease the width of microstrip at the pin?
Yes, it is a common problem, especially in routing of big BGA packages, where pad/ball pitch is rather small. As long as the narrower section is shorter than a quarter of shortest wavelength of your specific signal, this won't affect much your signal integrity (shape of waveform). 

Regarding the grey semi-circle, you need to consult with user manual for the tool you are using.