First I ever heard that. Everything I ever heard supports GR making the rule after the TM. It's not a "conspiracy theory", it's a sober account of the reason the rule came to be. Not that I ever saw any reason to respect such a rule...
I just looked this up for the project I'm working on, and everything
, including Jefferie's account, that I found about this dated the four rules to The Motion Picture
, well after the Tech Manual was made.
Considering that two of these rules were broken by the Original Series itself (SS Aurora), and then very quickly broken in The Next Generation, I would say that they have little to no bearing on anyone involved - official or not - in the design of starships for the Trek franchise.