Replace Recovery HD with a “bootable drive” formatted partition? A while ago, I had the idea to use the bootable Mac OS X USB drive-making procedure on a hard drive partition, so that I could basically have a version of the “Recovery HD” that doesn’t need to download Mac OS X every time. Then I realized that since I have that partition, I have absolutely no use for the original “Recovery HD.”

I was wondering, is there a way to actually turn my new partition into the official “Recovery HD”? As in, invisible during normal computer use but boots when ⌘+R is held during startup?
If you've installed Yosemite it will automatically have created an invisible recovery partition and so you may as well delete the recovery partition you created. Keeping a copy of the Yosemite installer on a USB stick is definitely a good idea though in case your drive ever dies or you need to perform a clean install (on an SSD for example).

Alternatively, you can hide volumes/partitions using the Utilities>Visibility function in Onyx.