I have actually fooled around with these numbers before but they seem to delay and lower the chances of rebellion to a degree but not get rid of them altogether. I had set all set prussia to -10 and compared it with when it was at its orriginal 2 and it actually made no difference. Then i lowered it to -4 to match the range of the highest value I've seen of 4 for portugal and it seemed to happen a lot less but it still does happen and at the most annoying times as well for some reason. I guess there isn't a way to completely disable rebellion from a mod approch.. :\

thanks for your feedbacks in anycase.