Correct Bad Fat Transfer Results with Blepharoplasty?

If your surgery was six months ago and things have reached a plateau, it is likely that you have a stable problem. The problem is how to treat it.
Firm lumpiness from fat injection to the lower eyelids is a common problem. In my experience it is usually necessary to remove the fat injection lumps directly. This is a tricky proposition, to say the least, because the lumps can be in all layers of the lower eyelid, from the epiperiosteal layer to the shallow subcutaneous layer, with the orbital septum and the orbicularis muscle in the middle.
Often, correction of the problem will involve midface elevation through a cheeklift, canthal restoration to support the amount of work to be done on the different layers, direct removal of fibrous fat injection tissues, possibly placement of new grafts. In our practice we typically use nontraumatized autologous fat fascial grafts (LiveFill) placed precisely, usually in the eye-cheek junction or the tear trough region. Or sometimes lumpy fat injection grafts can be removed directly through a transconjunctival approach or directly through the skin through tiny incisions, it all depends.
A traditional blepharoplasty usually involves reduction in fat from the lower eyelid, which would not typically deal with the fat injection lumps.
Your case underscores two points. First is that the lower eyelid is an unforgiving anatomic area. Second is that patients should have great caution before undergoing even seemingly minor procedures such as fat injection to the lower eyelid.
It never hurts to seek several opinions from plastic surgeons with special interest in the midface (i.e. cheeklifts, revision lower blepharoplasty) before proceeding with this next very critical step.

  Yes.  This is an option for you.  It will require marking of the fat lumps and tedious dissection and patience by your surgeon.  There is no right time to do this but at 6 months, I think you have been sufficiently patient for improvement.  I would seek out an oculofacial surgeon listed by ASOPRS.

Fat transfer is a well established method of restoring volume to the face. The amount of fat survival depends on technique of harvest and injection. Technical considerations may affect volume loss, symmetry, and need for further revision.
The advice of your surgeon on the fat transfer should be heeded. Nodules arising from fat necrosis may ultimately subside or may remain permanently. If your surgeon believes they will remain permanently, the best option may be to surgically excise the lesions with a blepharoplasty type incision. Be advised that there are inherent risks associated with a surgical approach including assymetry, scar tissue, eyelid retraction, unsatisfactory results, and need for further surgery. An experienced blepharoplasty surgeon is advised.