Add-Type -TypeDefinition @"
using System;
using System.Runtime.InteropServices;

public class DisplaySettings {
    [StructLayout(LayoutKind.Sequential)]
    public struct DEVMODE {
        private const int CCHDEVICENAME = 32;
        private const int CCHFORMNAME = 32;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = CCHDEVICENAME)]
        public string dmDeviceName;
        public short  dmSpecVersion;
        public short  dmDriverVersion;
        public short  dmSize;
        public short  dmDriverExtra;
        public int    dmFields;
        public int    dmPositionX;
        public int    dmPositionY;
        public int    dmDisplayOrientation;
        public int    dmDisplayFixedOutput;
        public short  dmColor;
        public short  dmDuplex;
        public short  dmYResolution;
        public short  dmTTOption;
        public short  dmCollate;
        [MarshalAs(UnmanagedType.ByValTStr, SizeConst = CCHFORMNAME)]
        public string dmFormName;
        public short  dmLogPixels;
        public int    dmBitsPerPel;
        public int    dmPelsWidth;
        public int    dmPelsHeight;
        public int    dmDisplayFlags;
        public int    dmDisplayFrequency;
        public int    dmICMMethod;
        public int    dmICMIntent;
        public int    dmMediaType;
        public int    dmDitherType;
        public int    dmReserved1;
        public int    dmReserved2;
        public int    dmPanningWidth;
        public int    dmPanningHeight;
    }

    [DllImport("user32.dll")]
    public static extern bool EnumDisplaySettings(string deviceName, int modeNum, ref DEVMODE devMode);

    [DllImport("user32.dll")]
    public static extern int ChangeDisplaySettings(ref DEVMODE devMode, int flags);

    public const int ENUM_CURRENT_SETTINGS = -1;
    public const int CDS_UPDATEREGISTRY = 0x01;
    public const int CDS_TEST = 0x02;
    public const int DISP_CHANGE_SUCCESSFUL = 0;
    public const int DM_PELSWIDTH = 0x80000;
    public const int DM_PELSHEIGHT = 0x100000;

    public static bool SetResolution(int width, int height) {
        DEVMODE dm = new DEVMODE();
        dm.dmSize = (short)System.Runtime.InteropServices.Marshal.SizeOf(typeof(DEVMODE));
        if (!EnumDisplaySettings(null, ENUM_CURRENT_SETTINGS, ref dm))
            return false;

        dm.dmPelsWidth = width;
        dm.dmPelsHeight = height;
        dm.dmFields = DM_PELSWIDTH | DM_PELSHEIGHT;

        int result = ChangeDisplaySettings(ref dm, CDS_TEST);
        if (result == DISP_CHANGE_SUCCESSFUL)
            result = ChangeDisplaySettings(ref dm, CDS_UPDATEREGISTRY);

        return result == DISP_CHANGE_SUCCESSFUL;
    }
}
"@

# change this to what you want:
[DisplaySettings]::SetResolution(1280, 720)