You might see notes appended to some procedures changing minimum arrival or holding Flight Levels dependant on met conditions ( e.g. QNH) but
AFAIK you can't just add your own corrections to an FL, if there's a FL requirement you need to stick to it, otherwise you are at risk of reduced separation with e.g. higher crossing traffic if you start adding your own corrections. If in your judgement you are really concerned about conditions you need to tell ATC you require a higher FL.
Looking at the Milan STARS (from the north) it looks like FL 130 or above will give you an adequate of buffer from high ground, even on a bad day, as long as you stay on the STAR.