I use blue painters tape on all my projects, tape the 2 pieces together than glue your pattern on them, to remove the tape off the plywood just apply a little heat on the tape with a hair dryer or a heatgun, if you have one and the tape lifts right off the plywood with little or no damage at all. If you glue the pattern directly on your project and you do any sort of fret work you have to sand the pattern off and that can get really tricky so for the cost of the tape I prefer to avoid the sanding part.
Good luck hope it clears it up for you.
.../Hans