Shrinking Reconstructed Nipple? Is it possible to have this operation done again, or is there a way to increase the size?

I am glad to hear that you are nearly completed with your breast reconstruction, but sorry to hear of your concerns.  It is common to have some shrinkage of the newly reconstructed nipple - typically between 30-50% of the immediate postoperative size.  I would continue to wait a few more months to determine your final result prior to any consideration of revision.  

In your instance, redoing the nipple reconstruction is certainly an option, but placement of a dermal graft or even an acellular dermal matrix (e.g., AlloMax, AlloDerm, etc.) should be entertained in order to add some additional size, projection, and longevity to the reconstructed nipple.  If you did have a very large nipple on the opposite breast and were agreeable to having that reduced, nipple sharing from that nipple to create a reconstructed nipple where it was absent is certainly an option as well.  Hope that this helps!  Good luck!