Don't think the throttle was modified - was it not the Fuel Control Unit (FCU)?
Yes i think it was the FCU and possibly also the ECA modded.
Also, I believe the reason the smoke mod took so long was that each aircraft is different internally and so the mod needed accurate drawings and bespoke manufacture.
As D Zero has already confirmed,the Hawks were jig built and the main production batch had very good ICY,so any hawk post XX162 (8th a/c ?)has good interchangeability (ICY)
Edit actually the component icy on the early Hawks is very good,but there are a few little differences externally.XX154 still has quite a few 'differences' LOL