We present a systematic structural, transport, iodometric, susceptibility and x-ray photoemission study of the Y( Ba-1- xPr(x)) 2Cu3O7-delta system for chi = 0.00, 0.025, 0.05, 0.075 and 0.10 with Pr3+ ( smaller in ionic radii but higher in valence than Ba2+) substituted at the Ba site. It is successfully shown that a higher valence cation can be substituted for a lower valence one. The rate of the Tc depression in these is observed to be much higher than that in the case when Pr3+ is substituted at the Y3+ site. This is explained as being due to a composite effect of the depletion of itinerant holes due to the progressive depletion of the oxygen content in the samples, the Pr 4f-O 2p hybridization and change in the in-plane coherence length (xi(ab)) resulting from change in the in-plane atomic distances, using Ginzburg-Landau theory.1932