The simple answer is anything can be made to fit, it's just how much fiddling it takes.
Best thing you can do is get as many dimensions of the parts as possible, for things like rearsets then make sure the securing bolts are the same distance apart, centre to centre, as on the fazer or you will need to make up plates to make up for the difference.
My experience of universal parts is that they are often not as universal as claimed or too compromised (so that they will fit everything) to actually do the job they are meant to do properly.
Can't speak for the rizoma parts though, have no experience of them. Having had a very quick google and look at their rearsets then the fzs600 doesn't appear to be on any of the drop lists as a bike they will fit so be very carefully before you buy anything.
All the best,
Chris