The Citation X is a fantastic aircraft, but not for the faint-hearted...
The CJ4 is a very simple little aircraft, easily flown single-pilot. I'm lucky enough to have great fun in the CJ series, both for business and pleasure.
Moving from one to the other is a big step, and I'd advise anyone needing to do that to engage the services of some experienced swept-wing, long-range people, rather than assuming that it's 'just a different type'.
In particular, this is not a transition to make on the basis of minimum action to satisfy the regulator... The X is NOT a typical-PPL machine, by any stretch of the imagination.