Similar to chemical doping, pressure produces and stabilizes new phases of known materials, whose properties may differ greatly from those of their standard counterparts. Here, by considering a series of LaFeAs_1-xP_xO iron-pnictides synthesized under high-pressure high-Temperature conditions, we investigate the simultaneous effects of pressure and isoelectronic doping in the 1111 family. Results of numerous macroscopic and microscopic technique measurements unambiguously show a radically different phase diagram for the pressure-grown materials, characterized by the lack of magnetic order and the persistence of superconductivity across the whole 0.3 ≤ x ≤ 0.7 doping range. This unexpected scenario is accompanied by a branching in the electronic properties across x = 0.5, involving both the normal and superconducting phases. Most notably, the superconducting order parameter evolves from nodal (for x < 0.5) to nodeless (for x ≥ 0.5), in clear contrast to other 1111 and 122 iron-based materials grown under ambient-pressure conditions.