Ah, what a breath of fresh air. After today's SDK Tools r9 and ADT 9.0.0 update that I talked about earlier this morning, I noticed another new feature in the SDK Manager that has been requested for years. As if the near-instant AVD restart support due to the new snapshotting was not enough of a present, developers can now edit properties of existing AVDs!
Before this update, once you've created an AVD, the AVD Manager did not let you touch any of its properties, forcing you to create a brand new virtual device for any tweaks. This was a giant pain for developers who needed to change or add a property, such as density, resolution, allocated memory, or API level.