I wrote a long-ish post about this elsewhere years back, but I can't find it. Anyway, TL;DR, I'd contend that so-called OFPF is often misunderstood. It shouldn't be viewed as something that's enforced in some ironclad way. Like, for example, thinking that if you have a 2-fret stretch (eg, 1-3 or 2-4), you always have to play it with 1 and 3 or 2 and 4. What it should really be viewed as, IMO, is being entirely comfortable with using any of your four LH fingers on any string at any position on the neck, as necessary. It's a matter of full-time four-finger availability. When 1-3 works better, do that; when 1-4 works better, do that.
And yes, also shift when it helps.
An aspirational goal is for fingering to be automatic. You read the notes off a page or think of a bass line, and your fingers make it happen without conscious thought.
In order to significantly realize this goal, one fingering system has to take priority over other options. There is not time to consider doing it two ways.
The primary system I use on bass guitar is my personal form of OFPF. Sometimes my fingering system breaks for a variety of reasons. When this happens, it's necessary to stop and figure out what to do. Lot's of options.
