The alterations in physical property across different space groups of the same material are sometimes conveniently reflected reflected by the crystal structure as a function of temperature. However, mirroring the physical property and crystal parameters over a wide range of temperatures within the same space group is quite unusual. Remarkably, Rietveld analyses of the X-ray diffraction patterns of PrMn0.9O3 (ABO(3)) nanoparticles (NPs) with a constant Pnma space group from 300 to 10 K could successfully predict the four magnetic phases, viz. paramagnetic, antiferromagnetic (AFM), ferromagnetic (FM), and spin-glass-like ordering. The increase in Mn-O-Mn bond angles and tolerance factor leads to FM ordering below similar to 400 K in usually AFM PrMn0.9O3 NPs. The concurrent decrease of lattice cell volume and Mn-O-Mn bond angles near the AFM to FM transition temperature (T-c) suggests that the AFM character increases just above T-c due to atomic deformations and reduced Mn-Mn separation. The predictions from crystal structure refinement were successfully verified from the cooling path of the temperature-dependent field-cooled magnetization measurements. A mechanism involving incoherent spin reversal due to competition between the neighboring spins undergoing antiparallel to parallel spin rotations was suggested. The structure-property parallelism was cross-checked with the A-site vacant Pr0.9MnO3.2 NPs.