We examine the possibility of influencing medium scale size (0.1~10 km) interchange modes in the high-latitude F region ionosphere by a high-power, high-frequency (HF) electromagnetic (''pump'') wave launched from the ground. The parametric coupling of interchange modes with the pump wave will occur near the critical layer where the pump frequency matches the local plasma frequency with the nonlinear Joule heating providing the dominant coupling mechanism. We find that the parametric excitation (or suppression) of the interchange process at high latitudes is possible, in the local approximation, for short wavelengths (k⊥LN≫1, where k⊥ and LN are the transverse wavenumber of the interchange mode and density gradient scalelength, respectively) using HF power densities (>10-6 W/m2) that are attainable by current ionospheric heater facilities. These power density estimates for longer wavelength interchange modes, i.e., for k⊥ LN≲1, are increased. The results are discussed in light of previous and possible future ionospheric heating experiments.