A taller tire will affect the ride height some and with that the weight bias of the bike so checking the sag won't hurt, but you will not deviate from the 30mm that you are already using, you will simply reset the sag to get the correct number. Along those lines sag needs to be set on flat level ground with the rider sitting in a natural riding position. These guys that set sag in a wheel chock or stand are getting false readings.
A taller tire may also affect the geometry as well, but the only way to figure out if the affect is beneficial or negative is to ride the bike with the new tire and make a determination. In most cases the profile of a 190/55 is so much better than a 190/50 that it is already going to be better handling all around. You gotta try it though. Don't just start making geometry adjustments because you think you need to, wait until you have a specific reason.