Attempting to swap them would likely result in:
* The rear blower not working in the front: It wouldn't have the power to move enough air through the larger front ducts. You might hear it struggling and possibly burn it out.
* Wiring incompatibility: The connectors are almost certainly different and won't physically match. Even if you could force them, the wrong voltage or amperage could damage the motor or other components.
* Control issues: The speed control circuits are designed for the specific motor's characteristics. The wrong motor would likely not respond correctly to the speed controls.
In short, while you might be able to *physically* make the motors fit in the wrong locations (with a lot of modification), it wouldn't be functional and could cause damage. If one motor is failing, you need to replace it with the correct replacement part for its location.