If the printed item is at least as strong as the ply and can be laminated onto the transom surface as well as the ply, it will work. If not, no, it won't. Ply tends to be much stronger than the material that is made from suggests. Giving it a coat of epoxy or similar to mount it and waterproof it strengthens it.
I imagine that mounting a printed plate would not have that effect, but it depends on the type and thickness of the plastic used. And the actual design - a ribbed plate with the ribs in the right place "might" be both stronger and more reliable, but does depend on knowing what the likely stress points are going to be before design happens.