Read original post at Matt Lacey's Blog
A few weeks ago I created some nuget packages to make it easier to work with the WMAppManifestFile, so you don't have to manually edit it.
Since then I've realized that to indicate that you want an app to use more meory if available or to require that your app must have more memory to run (and therefore can't run on low memory devices) also requires manually editing the WMAppManifest.xml file.
So, as you may have guessed, I've built somme nuget packages that can set this up for you.