Yes it would be nice if they defined “service” and there are many different definitions. For example, and since many people like to use Merriam-Webster for their definitions, another is as follows.
As it happens, just as with TREC, TSBPE will define it clearly when they send the offender a “cease and desist” notice.
Re your hydrostatic testing comment this was the TREC Advisor newsletter where they covered that back in 2016 https://www.trec.texas.gov/sites/default/files/AdvisorMay2016.pdf . Over the years I have heard that TREC will not pursue an Inspector just for starying into another licensed professions work. However over the years we have seen various cases where they will including the latest one not long ago where an Inspector was tagged for supposedly performing a gas line pressure test. All of these incidents where TREC pursued the Inspector appear to have been complaints from all sides of the RE transaction.
As for sewer scoping, and any of your other examples above, every Inspector needs to do their own due diligence before they act and provide services beyond what is required by the SOP/laws/rules. Part of that due diligence is becoming familiar with the laws of other licensed professions. Once they have done that they can then make their own decision if they want to take on any liabilities for those actions, including the liability of being called on the carpet by another licensing agency. In the end the Inspector only has themselves to blame for any issues they cause!