I just want to report that today I did successfully convert my iHAS424 into an iHAS624 using the codeguys stock 624 B firmware (thanks to NewFish).
Smarterase is confirmed working, although I think this is already a feature of the 424.
LabelTag is confirmed working, although a little cumbersome to use, however I am amazed by the quality of the print. It is surely a cheap way to label your discs without having to pay extra for Lightscribe. For those new to LabelTag like me, I would just like to add that this is for single layer discs only, and DL is not supported.
Lightscribe is already feature in the 424, so I didn't test this yet, I presume it will work because the 424 has hardware support for it. I don't have any close retail stores with Lightscribe media available so I might order some online.
Thank you to everybody who contributed!