Is it legal for me to braze my new catalytic.

Virginia is very strict about safety inspections. If you are sure the brazing material is of the same quality or better steel than the exhaust, that would be a requirement for a good seal. Also, you must be able to make it all the way around the pipe to have a continuous weld. This ensures that there will not be any leanks. If the brazing material looks significantly different from the exhaust pipe, that might raise a red flag. Another issue would be a sloppy or incomplete weld. If it looks sloppy the inspector might not pass it. If you are a good welder and can make a nice complete weld all the way around the pipe, it should be okay. Remember that any leaks in the exhaust will come up in the emissions test and it could possibly fail it.