As always, there are tricks around this issue. Since you can tell iOS 6 to download a playlist, you can just create a single-track playlist and download a track. When it comes to deleting tracks, however, it's an all or nothing proposition: You can remove all your local music by going to Settings -> General -> Usage -> Music and swiping to delete the items there.
A is for Accessibility
Accessibility is one of the more overlooked aspects of iOS, but it's key for a device that relies so heavily on the touchscreen. iOS 6 brings a few enhancements to accessibility, but the most significant by far is Guided Access.
Guided Access Originally designed as a way to help make the iOS devices friendlier to kids who learn differently, Guided Access lets you disable certain parts of the device so that kids don't accidentally trigger something they're not supposed to. (Sure to be a boon to every parent who's come back to find that their kid has accidentally deleted their last five emails.)
Guided Access gets enabled in Settings -> General -> Accessibility, under a new heading titled Learning. Once you've enabled it, you can summon it from any app by triple-clicking the Home button. (If you'd like to have options of which accessibility features are available by triple-clicking, you can choose from the Triple-click Home section under Accessibility--pick more than one feature, and you'll be presented with a menu when you triple click the button.)
By default, Guided Access disables all hardware buttons when activated. Via the Options button that shows up when you activate it, you can also disable the motion or touch functionality. Best of all, you can--in a simple but very cool interface--disable certain onscreen controls by simply drawing around them. So if you just want to turn off a button that lets kids view other screens in an app, you can do that. Those areas will be shown with a gray halftone and won't respond to touch.
(Be careful, though, because Guided Access performs its magic based on physical areas of the screen. So, for example, if you disable a toolbar at the bottom of the screen, and the device is then turned to a different orientation, it's now the side of the screen that's disabled. Likewise, I found the hard way that disabling part of the bottom of the screen also disabled the bottom row of the onscreen keyboard too.)
To disable Guided Access, you simply triple click the Home button again. That's gauged to be tough for most kids to stumble across, but if you're concerned, you can also set a passcode that must be entered to disable Guided Access.
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