probably not wise doing S-turns in a PA38
True but over specific. It's not wise doing ANYTHING in a PA38, and least of all trying to fly the thing. Maybe sitting it in it parked on the ramp, watching the planes on the runway, with a good book and a glass of something, would be OK, though a deckchair would do the job better.
Fwiw, I retrim frequently - the pitch control in my plane (182RG) is very heavy and it is tiring to be even ever so slightly out of trim. With my newish autopilot (STEC30), if I want to use it in climb or descent, I have to trim for rate of climb (or descent). It can be done but it takes a VERY fine touch. The tiniest possible movement of the wheel makes a noticeable difference to attitude and hence speed (both vertical and horizontal).
But in the Pitts, I touch the trim only when entering the pattern, to trim for final speed. Oh, and when it goes to full nose down all by itself, to yank it back to the right place, which it invariably does after a tailslide.