  Compelling efforts to improve the critical temperature ($T_{c}$) of
superconductors have been made through high-pressure application. Understanding
the underlying mechanism behind such improvements is critically important,
however, much remains unclear. Here we studied ortho-III
YBa$_{2}$Cu$_{3}$O$_{6.73}$ (YBCO) using x-ray scattering under
hydrostatic-pressure (HP) up to ~6.0 GPa. We found the reinforced oxygen order
(OO) of YBCO under HP, revealing an oxygen rearrangement in the Cu-O layer,
which evidently shows the charge transfer phenomenon between the CuO$_{2}$
plane and Cu-O layer. Concurrently, we also observed no disorder-pinned charge
density wave (CDW) signature in CuO$_{2}$ plane under HP. This indicates that
the oxygen rearrangement modifies the quenched disorder state in the CuO$_{2}$
plane. Using these results, we appropriately explain why pressure-condition can
achieve higher $T_{c}$ compared with the optimal $T_{c}$ under ambient pressure
in YBa$_{2}$Cu$_{3}$O$_{6+x}$. As an implication of these results, finally, we
have discussed that the change in disorder could make it easier for
YBa$_{2}$Cu$_{3}$O$_{6+x}$ to undergo a transition to the nematic order under
an external magnetic field.
