Are you able to add more porcelain to existing porcelain veneers to close gap?

That's a good question, it is possible to either bond porcelain or composite to existing porcelain veneers.  A skilled dentist can probably use composite in the office as a faster, more economical option, as long as it's a good, high-quality composite.  Another option to close the gap is to redo Orthodontics - braces or Invisalign.  Invisalign might be a better option for you so that you don't damage the porcelain.  And then have the orthodontist make you both a fixed retainer wire bonded onto the back of the teeth as well as a removable retainer or nightguard.  An alternative is to redo the veneers to close the gap, but be careful because you will have size discrepancies and asymmetry, particularly the width of the teeth since you are dealing with spaces.  So you may end up with large teeth.  If you decide to go this route, be sure to have your dentist obtain a diagnostic waxup prototype prior to treatment so that you can see what the outcome will be.  And then after the new veneers are placed, have an orthodontist also bond a fixed wire retainer and a removable retainer and/or nightguard so that the teeth don't move again.  Best of luck!

Hi, typically without changing the veneers you are unable to close the gaps with composite resins.However you may want to consider having orthodontic treatment and having a fixed retainer placed in the back of the teeth to keep the teeth from separating. It would be a much simpler and straightforward option and easier for you. Consider using Invisalign for this treatment. All the best.

For longevity and the best esthetic outcome, I would recommend new veneers. You may be able to bond onto the veneers, but that usually falls off.

Hi:Bonding which is a resin material can be added, however porcelain can not be added without using an oven.Best,Dr. Maddahi

Unfortunately you can not add more porcelain to existing veneers. You also can not add composite bonding on existing porcelain veneers. To close the gaps, either Invisalign or new veneers. 

Hola,
es mejor retirarlas pues al adicionar mas resina a los dientes pueden cambiar de color y no es recomendable adcionar resina sobre otra resina.