From my experience as a vet tech, I would say yes that can be harmful but I am sure there are plenty who would disagree. The effects may not be immediate but vaccines are powerful drugs and they are full of toxins. They should only be given with great caution and discernment at the proper times, separately and only to healthy animals during a time of no stress.
That being said doubling up on rabies vaccines is actually quite common. Dogs with unknown histories are always treated as un-vaccinated and given the full load. A practice I think absolutely needs to be done away with.
If that did happen, you can't go back and change it so don't stress about it. That won't help anyways. Just keep an eye out for anything strange down the line in regards to the immune system. You may want to check out the Jean Dodds recommended vaccine schedule as well. http://www.itsfortheanimals.com/DODDS-CHG-VACC-PROTOCOLS.HTM
Personally I have had good results with using Thuja after vaccines.