By their nature, hot tap nozzles may not be as strong as regular API 650 nozzles. Yes it is per code but why risk it? Some owners and jurisdictions specifically require hot taps to be replaced at the next outage. Especially when live piping is attached and high shell stresses may exist. There must be a reason API 650 does not use the API 653 hot tap weld details. API 653 does not use API 650 details because it can not and a 3-way tie in to the surface of the shell plate just does not seem to me to be as good as a full pen weld. Personally, I'd replace the nozzle neck using API weld and nde details and put an API repad on it. API 653 is silent on the service a hot tap nozzle can be used for, it only provides guidance on the installation of a hot tap so it is up to you and the judge you are in front of to interpret or decide what was intended. Perhaps a 6" nozzle is small enough, the actual weld is high quality everywhere, there are no notches to increase stress, corrosion is not an issue, thermal and other piping stresses are low, your tank is not in critical service, the tank will not settle, the shell plate has no laminations or other internal defects, the full pen weld to the repad is an equal replacement, etc etc, and your risk is small. I'm conservative, perhaps too much so, but your tank is a very large capital investment meant to last for years under obvious and unforeseen conditions. You have little legal risk because you did it per code but again why chance it? How much will it really cost considering the big picture and how easy will you sleep at night?