Well, the desination "350" is nothing more than a Salesname, officially its just a Facelift of the KA300.
The Official Name of a KA350 is B300, the KA300 has as ICAO Designator BE30.
A "350" Typerating will be under EASA valid for all 3 Variants : 300-350-1900, but you Need Difference Training when Changing your ride.