I was at the Dealership the other day talking to a customer at the Parts Dept. A Mercedes mechanic overheard me tell a customer how to set up to change out his fuel pump . I said if you turn it a few degrees past TDC you can back it up" On that sentence and the mechanic came excitedly running over and said "See, don't listen to just anybody. He's not a Mercedes employee" The customer fled and the mechanic walked away.

I saw him later as I left. I smiled and I intoduced myself and told him I am an engineer by profession and I asked him politely, "Why can't you turn an engine counterclockwise.What's the real reason" He mulled it for a minute...I asked him, "ever see an engine backfire?" He was young--some of these modern gassers never backfire...
We went through the whole scenario about the tensioning device being on the soft side of the belt-and might have to work harder, but otherwise, there is no difference except the oil pump isn't going to put out pressure.
I wouldn't run the engine ccw. But you can turn it ccw.
At least he was man enought to apologize.