Is it actually possible to stall in the 'conventional' sense (ie, not g-stall or shock stall) an a/c fitted with a modern stall protection system.
Yes.
Even aircraft fitted with a stall pusher may actually have it set such that it does not trigger until an angle of attack higher than the "natural" stalling angle of the wing. This would be for a case where the natural stall is relatively benign (and basically certifiable) but there is a requirement to prevent excursions into an angle-of-attack regime where a deep stall is possible. This applies to (some) T-tailed designs.
There's no huge difference aerodynamically between what I think you're calling a coventional stall (deceleration in essentially level flight at nominally 1'g') and a "g-stall" (either deceleration at elevated 'g', such as the decelerating turning stall used for civil certification, or a progressive increase in load factor at constant speed, such as used for the buffet boundary penetration tests in civil certification). Provided tha Mach and altitude are similar, it doesn't matter much what the load factor is (allowing for issues such as wing twist induced by load and inertia distribution, of course).