It _is_ possible to get green sticker bikes legally plated, and I know someone who did this on a 450X and CRFF230 both. There is a certain shop in CA, that has worked out the hassled of dealing directly with CARB, and they basically get your bike re-certified with CARB. You even end up with a new VIN when it's all over. Problem is, it is about $2000 at the shop, plus figure $500 for complete switchgear, lights and all the trimmings to meet the letter of the law.
The short of it is that it's not going to save you anything over buying a KTM, but if for some reason you're set on a Honda, it's possible to do. Also, the shop can only do a fairly low amount per year, so if it's not early in the year, you're probably waiting till the next.