You know, sometimes we just get way too technical about all this cake stuff. May I suggest you use your fingers (either with or without a glove on) and scoop a little icing onto one finger and delicately cover the corners that you are worried about. After the icing crusts you can smooth with the Viva paper towel technique.
My suggestion would be to definately have the cake cold-maybe even slightly frozen..........makes it much easier to ice and get sharp corners. If needed, put it back into the freezer after you are done and shape with your fingers. I work mainly with fondant- and I decorate all of my cakes cold........Hope this helps!
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