Sorry Voodoo can't be done.
If I remember it was stated specifically that if you change your GT during an HLC then they will not be added together no matter how simple and straightforward it might be.
If an excpetion is made in your case then everyone else will see that as being a precedent set for the future and also those that were affected in the past HLC's would see that as a bit of a snub.
Member of Racing 2 Perfection, R2P
GT - R2P Flying Scot
My Only Livery attempt