No the 4.2 X150 XKR never had any major changes, they came about with the introduction of the 5.0L. The 4.2 X150 had a few major changes from the X100 such as VVT and the paddle shifts it is pretty much bullet proof.
As to a Zircon blue convertible, well I'm biased... very few were produced it was only available for one year and it was replaced by Frost blue which is pretty close. There are darker shades such as Kyanite