You can't. You can use the CSS you create, but you cannot map the keys to your settings.
It works for the heading, because that does not need additional settings. Just change the tag to <h_>. You can change the code afterwards, but you already do that.
I usually use just a <p> class for indents...
You could create an issue on the tracker for this enhancement. If Valloric feels like it, perhaps he will incorporate it. Then again, perhaps he thinks it is gold bidet...