Can I crush candy canes and put in brownie batter before baking? Don't want to sprinkle on top...

You sure can. and that's a very festive idea this time of year. I put all manner of candies, nuts, other add-ins into brownies for variation. I'd be sure not to crush them too small. You want the eaters to know what's in there.

Probably (I've never done it.). David Lebovitz makes brownies with Altoids. http://www.davidlebovitz.com/2008/11/baked-altoid-brownies/