Yes, Platinum Desk, Preppy, Plaisir, and Prefounte fountain pens have swappable nibs.

The Platinum Preppy, Plaisir, and Prefounte pens all have the same style grip section, so to swap those, just unscrew the grip section and screw it back into the pen body you prefer.

The Platinum Desk fountain pen uses the same nib as the other pens, so to swap that, just pull the nib and front half of the feed straight out of the pen. If you're having trouble, try using a piece of tape using the same technique as for replacing a Lamy nib. Be aware that the stem of the feed will also come out with the nib. Do the same thing to your other pen and just push the new nib into the Platinum Desk fountain pen to install it.