Hi Atari800XL,
well you can't change the DPI inside a PE after booting. But you can force it before boot inside the registry.
_RegWrite('HKLM\PE_DEF\Control Panel\Desktop', 'Win8DpiScaling', 'REG_DWORD', 1)
_RegWrite('HKLM\PE_DEF\Control Panel\Desktop', 'LogPixels', 'REG_DWORD', 168)
_RegWrite('HKLM\PE_DEF\Control Panel\Desktop\WindowMetrics', 'AppliedDPI', 'REG_DWORD', 168)
_RegWrite('HKLM\PE_SOFT\Software\Microsoft\Windows NT\CurrentVersion\FontDPI', 'LogPixels', 'REG_DWORD', 168)