Trimming is no sweat but you have to let the decal dry 100%, then do all cutout trimming with a brand new #10 X-Acto razor knife blade. Any minor ragged edges or minor edge overfalls can be eliminated with a decal settling solution such as Solvaset (or whatever product the decal manufacturer recommends).
I didn't watch the video all the way through, but the final step needs to be some kind of clear protective spray overcoat such as polyurethane or acrylic lacquer. The finish needs to be chemically compatible with the decal substrate so wrinking or melting doesn't occur.
Great Site, Thanks for the info Brian. George T