Is that supposed to be on permanently, regardless of other splinter configuration actually needing it or not?

I was really suprised when I pasted from a long inserter onto a short inserter, and suddenly the arm length changed.
Nowhere does it say that it enables it, I had to look into the code to see what was going on.

Being used by logistics and later fishing. But good catch might need to out a check in there somehow.

I'd say that it'd be better to put it in those mods, or only apply the change if those other mods are active.
Alternatively, make it a full feature and add a gui that controls it or smt.

Nope

Possibly in mods but gui no