The critical rates just adds up. So we'll have 100% critical rate when attacking against enemy weak points with this skill. The 50% seems to be excessive, but it is said that this extra 50% is intended to use with a certain S4 augment. This augment lowers critical rate by 50%, but at the same time increase the amount of critical damage by 6%. This will be a pretty good combo, as long as we attack the weak points.
I'm not sure if this S4 augment has already been on the global server. As you know, we must know the exact name to search this on the visiphone, but Arks Visiphone (NA) seems not to have this on the list yet. Speaking from the naming conventions of S-grade augments, I guess the name will be something like S4: Skillful Balance, but searching that name hit nothing.
And speaking of the notification, thankfully this was not a silent update. They've announced this in a section titled additional adjustment.
Better move, I'm glad about it