Can a front motor mount that has gone bad be responsible for a shaking at idle?

If so, is it possible to trash a motor mount by removing it? I first moved the flange that connect the block and mount around a great deal, and then I went on to remove and reinstall the whole thing.

I recently installed a nice new header. Doing this forced me to first unbolt the connecting flange (from the mount to the block) and move it around to get the primaries on. Then I realized that I had to pull the whole mount to get the rest of the header on. I dremeled a bit off of it for good measure and put it back on after I got the header assembled.

I noticed the rubber was cracked on both sides, and I reused the main bolt that goes through the rubber that my helms told me to replace. I tightened the mount down first, held the flange in place with the block bolts loosely in the block, tightened the bolt through the rubber, then tightened the block bolts.

I have no idea if that was the right order, it was getting dark and I was rushing. Could that have messed it up?

The short of it is before my header/motor mount removal/installation my idle was fine. Now I get some shaking. I don't think the header, as tight as the packaging is, is hitting anything. But I dunno.