Theoretically: it is possible when the bone has fused again 6-8 months to a year after the zygomatic osteotomy.
In practice: you will very likely ruin your chances to get Lefort III done. It would be very difficult to find any surgeon that would be willing to do that. Since the zygomatic osteotomy is going to give some forward/sidewards increase in projection. Perhaps in places where you don't necessarily need most increase in projection. (And places where you perhaps want an increase in projection too won't get it). But it is going to give an increase in projection in some places. (In my face I have the fuller low round cheeks someone described too. Not the high arched zygoma's I had really wished for. If I could undo it, I would do so).
So to then get a Lefort III is setting yourself up for problems that no surgeon will want to get involved in. Since you will get over-the-top enlarged cheeks in those places that have already an increasement in projection after your initial zygomatic osteotomy, if they are projected more with another surgery (the Lefort III). No surgeon will want to do that with the prospect of possibly creating a fake looking result. Even if you still have very recessed places in your face/along the orbit, next to the projected places. Pick the right procedure immediately. Or go for the Lefort III first since it will give an increasement in projection in all those areas. And if you then still feel you need a little bit of an increasement in projection of the lower cheeks, then you can see what you can still do (and whether any surgeon feels a zygomatic osteotomy is still possible without giving overprojection in some places of the cheek or you can look into Coral paste).
