I have certainly done this. Yes, I snipped the threads, inserted the stems and reappliqued. It was not 18", more like 2", because I did the applique equivalent of backstitching to be sure th snipped seam was still solid. The idea is to snip the thread only once, then unsew as little as possible. Because I am far from perfect, I have become something of an expert on fixing my errors. I know several people who take the whole thing out and start over. I finish quilts, lots of quilts.