Crowns and veneers can be removed, however because they are bonded to your teeth, they will probably require cutting them to get them off, and immediate replacement with new restorations.
There should not be any problem with the adjustments or the re-glazing process weaking the veneer. Just make sure you are happy with the veneers before they are bonded onto your teeth.
Typically on front teeth, you will be fine with a veneer covering the tooth after a root canal. The exceptions may be if the tooth is fractured or has developed further decay. Often times the less done to front teeth the better.
This situation can be very frustrating for everyone involved. The simple answer to your question is yes, your veneers can be removed. However depending on the type of veneers done, your teeth very well may need new ones to cover your existing tooth. Some simple steps may help correct your issues. 1. A wax model of the final veneers can be done by a lab to show you how the teeth will look when you are done as well as allow you to wear temporary veneers that will mimick the final outcome. This will also allow you and your dentist to discuss the color that you prefer. 2. Before bonding on the new veneers you should have ample time to inspect them to make sure they are to your satisfaction. Good luck.
The safe play would be to let your dentist order a new set while you continue to wear the previous set. Then continue along your path of treatment.
