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You can install a third party launcher on Glass. Here's one that lets you switch between launching APKs and the standard Glass interface pretty easily:

https://github.com/kaze0/launchy

There's also a Mirror API based Glass app that lets you launch apks, but it's a bit more work setting up. It actually requires you install a couple APKs as well: https://pontedivetro.appspot.com/

I've only run APKs in USB debug mode, but the main "OK glass" screen is just an Android app, which I think is started via an Intent, so I suspect you could hook this and override it.

There is a custom launcher on github called launchy.