I just did that replacement this morning on my daughters Zetec. This one had two 10mm bolts holding it in. I had to loosten the idler pully to get at one of them & put a wrench on the tensioner pully to get at the other. Overall it was fairly easy with a 10mm gear wrench.
As far as the torx bolt, you might have to get a bolt extractor from Home Depot to remove that thing & replace it with some fresh hardware.