Can I have my porcelain veneer re-cemented?

Unfortunately,  it is very difficult to remove a porcelain veneer once it is bonded in without fracturing it.  That being said,  there is a hard tissue laser on the market called a Lightwalker that has a setting that will allow the dentist  to remove a veneer without  harming it.  There are very few dentists that own this laser, but if you can find one in your area they may be able to get it off.  I have one in my office,  but have not had to use it for this yet.   I have seen it performed though and it worked beautifully and took about 3-5 minutes to remove.  Good luck.  

Unfortunately once a veneer has been cemented with a permanent cement it will likely need to be cut off to remove it. You'll have to have a new one made. Panavia is an excellent cement, however it is not recommended to be used to cement veneers because it is very white and opaque and it will change the color of the veneer. Veneers are very thin and translucent. I bet the veneer looks whiter.
Good luck
Dr. T

Yes, you should have it re-cemented as soon as possible.  Veneers can be fragile and you don't want it to break and have to have a new one made.  Call your dentist ASAP and it's an easy procedure to have it "glued" back on.