Question 2. - Nothing to add
Question 1. - Split Switch
In light A/C you will find usually either a cut-off switch or CB easily accessible or the mentioned split switch.
In the split switch - if you look at the electric wiring diagrams you usually see that one part activates the trim motor while the second part activates the clutch to the trim wheel. This, as you mentioned to avoid trim runaway. If any one of the switches would fuse together the contacts or shorten in any other way the missing input from the second switch would avoid the runaway.
The AFM usually explains that.
On some A/C you check this when checking the Autopilot e.g. PIPER SENECA III. Push only the left part of the trim switch forward or rearwards and try the manual trim wheel. No difference to manual operation should result. Try the same with the right part of the switch you should note that you need more force to turn the trim wheel because the clutch is now closed and you also turn the electric motor. (Derived from Piper Seneca III Information Manual Section 9 Supplement 8 for PA-34-220T)
CAUTION: No liability or any responsibility can be derived from this tip in any circumstance. Only the official source such as AFM/AOM shall be used to perform such check.