you just need to craft the AE2 certus quartz into blocks, and then craft back into GT certus.

I can't seem to replicate this?
The most I've got out of this is 5 extra certus quartz per block and it doesn't seem like this can be transformed back into AE2 Quartz making it less valuable for this purpose.

you can grind the greg certus back down into AE2 certus dust and use it for crystal transformation.