No, the piping gel does not get hard. The point is to gently transfer the piping gel to your cake so you can then pipe over the gel with your buttercream icing.
Make sure your icing has crusted well before attempting this transfer.
Print your message in reverse (or just flip over your printed page so you will be piping the message in reverse).
Place a piece of parchment paper over your flipped/reverse image.
Load a bag with a few tablespoons of piping gel and a tip 2.
Trace your flipped/reverse message in piping gel, making sure to touch your tip down ONLY to start and stop your lines...keep that tip elevated to let the gel fall out in a nice 3D line. Do not overpipe. Keep each stroke of each letter separate.
Once piped, pick up your parchment paper, turn it over, and position your message over your cake where you want it.
Gently set the parchment down on the cake and GENTLY use a decorator's brush (small paintbrush) to trace the entire message. The point is to be gentle enough to transfer the gel to the icing but not smush it so it's just a smear of piping gel. You will be able to see when the gel has adhered to the icing.
Once the message is completely traced, pick a corner of the parchment paper up and carefully peel the paper off the icing.
Voila! Your message is now transferred onto your cake so you can pipe over it with buttercream icing. Your printing is perfect and no one is the wiser!