May be different in your state. In TX and most states next to us, the stamp between structural, mech, civil, blah, blah, are all the same. Meaning you can "legally" (although highly frowned upon) stamp a structural drawing if you are granted an engineering license from the state and "feel competent" in material being stamped.Out of curiosity, what do you mean by the stamps not being competency based? It seems to me that to be licensed, the Principles and Practice of Engineering exam tests one's competency. PDH hours for license renewal test continued effort to remain competent.
The only thing I could see is something like retesting every 10 years or so, possibly with a shorter, online exam. Say, retest the depth portion of the PE exam every 10 years.
A lot of states also do not require your ABET accredited engineering degree to match the competency of the exam you take meaning you could get a mech BS and then take the elec power exam while getting your years of experience working under a structural engineer.. Think TX would list your competencies mech/elec in this case..
Haven't done a deep analysis or been curious enough to call the texas board though so further hypotheticals are encouraged. Know if you pass an additional test, you just call them, send them something from NCEES, and then they add your new competency (feel there should be another experience wall there..).