THIS IS FOR CYANOGENMOD ROMS ONLY!!!
Here's an easy way to trick your Optimus M or other MDPI based device into using those nice HDPI themes found on the Android Market and all across the web!!!! I have tested this on over ten themes from the market including Epic Blue, Stygian Blue Fade, ICS for CM7, and many more.
The File Manager Way:
1. Navigate to /system/ and find your build properties
2. Copy them to your sd card and name the ones on /system/ build.prop.bak
3. From your SD card, using a text editior of choice look for the following value:
You may notice TWO lcd lines in there but we only need to change the one mentioned!
4. Change the value to 140
5. Copy the new build.prop to /system/ and reboot.
6. Apply the new HDPI theme.
7. Now delete the build.prop and change the origionals back to build.prop
8. Reboot and enjoy your new HDPI theme
The FIRST time you do this MAKE SURE YOU MAKE A BACKUP!
Note: It will make the process easier if you keep the modded build properties you've made with reduced LCD for future use. This will save you lots of time when changing themes as you already have a set of properties with the LCD modded.