The stall strips are used as a final fix once the prototype is flying. The Airtourer is a good example. Without stall strips (per the T6 variant) it has quite a sharp stall and based on one example of the type, even flaps up & power off, the stall is accompanied by an uncommanded roll to a bank angle of around 20 deg or so. Not so with other Airtourer variants. With stall strips the resulting early separation at the wing root causes sufficient buffet that it is accepted as natural stall warning - the tail happened to be in just the right position for the wing wake to impinge on it - the buffet still has to occur within 5 to 9 kts of the stall to be accepted as appropriate warning.
I don't recall any examples (I lead a sheltered life so only know details of those types that I've worked with) where the strips have been added just to generate sufficient buffet for natural stall warning - but no reason why not if that is the requirement.
The last military trainer wing that I designed (unfortunately only got to prototype stage and not into production) had wash-out plus different aerofoil sections root to tip. During wind-tunnel tests we saw the need to modify it to ensure stall characteristics would be acceptable - so we added a wing root cuff (it had been on our list from when we did the early analysis anyway). We didn't want any more wash-out nor did we want to change the aerofoil sections - one factor being that detail design was well advanced by then.
Reminds me of the MB326 fleet with the wing rebuild. Afterwards they needed "sharks teeth" on the leading edges to eliminate a leading edge laminar separation bubble and it then reverted to the turbulent separation further aft on the wing as per original production.
I've also added stall strips further outboard from the root to eliminate wing drop at the stall. It was enough to induce earlier separation at mid-semispan - less effect on stall speed. And that was with a constant chord wing, no wash-out and same aerofoil.
(I apologise in advance to anyone who thinks that my students get this sort of detail at a standard briefing)