You need to do a deck switch so that they think the gimmicked deck introduced is the same deck that was used previously in other effects that they were handling, shuffling, etc. If you like to use Shadow Masters, then you need to accept that any new deck introduced that doesn't look the same will be scrutinized. I'd suggest letting go of the style the Shadow Masters provide and instead focus on what you can do to make the magic you're performing the most deceptive. In this case, it's making the audience belive the gimmicked deck is the same regular deck you used previously.
As far as a deck switch goes, the easiest thing to do is do some effects with your regular deck, then put the cards away and do something else. Then take your gimmicked deck out to show them "one more things with cards."