If we want to add a half bath to an existing home in Austin city limits (built circa 1935), which will require the addition of an extension of the plumbing, will the code requirements make us update all the plumbing in the whole house? Same question with the electrical.
You shouldn’t have to re-wire or re-plumb the existing house. On the other hand, if there is a “dangerous condition” that makes the house unfit for occupation, then they will make you fix it. So if there is something seriously wrong with your main panel, they won’t let you add circuits to it until it’s fixed.