So Valve added a lot of advanced settings recently, and I'm not sure if anyone's made a post about this yet, but I figured I'd share since the setting I just found was pretty neat.
Having played enough Dota with the double-tap to self-cast settings on, probably everyone has experienced the horror of situations like the one ArtStyle encountered when he accidentally self-graved instead of graving his carry. Well, using a combination of 3 new settings, I've found that you can prevent those situations from ever happening again while still having the ability to self-cast without having to target yourself.
Here's what you do: Under the Options tab for Settings, you tick the box next to "Double Tap Ability to Self-Cast" (to enable double-tap self cast) and the box next to "Smart Double Tap" (this enables you to simply hold Alt + the spell you want to self-cast if you want to self-cast, instead of having to double-tap). Then, click on the Advanced Options under the Options Tab, and under the Miscellaneous section on the right, move the "Double-Tap Self Cast Timeout" scrollbar to a value of 0. The combination of these 3 settings means that double-tapping a spell will never self-cast ever because the timeout value is 0, but you can still self-cast by holding Alt + the spell you want to cast. That's it! Hope this improves your gameplay.
TLDR; To disable double-tap self cast but still have the option of self casting without targeting, enable "Double Tap Ability to Self-Cast" and "Smart Double Tap" under Options, and set your "Double-Tap Self Cast Timeout" under Advanced Options to 0. This will allow you to self-cast by holding Alt+Spell, and double-tap will never self cast again.
