While this technically is possible, we think in most cases it's not a great idea to try re-magnetizing a fridge seal with a neodymium magnet. A lot of times problems with fridge seals come from the seal being dirty or deformed in some way, not because the magnet got weaker over time. Rubbing a neodymium magnet over your fridge seal can either demagnetize the seal completely or weaken it, and end up making the problem worse.
We discuss this in greater detail in our blog, check out Re-Magnetizing Refrigerator Seals for a more detailed explanation.