That only applies to steel-frame guns. Airweights weren't rated for +P until the late 90s when S&W started using the J-Magnum frames.

You likely won't get a catastrophic failure, but +P will accelerate wear, potentially causing some frame stretching that could lead to timing issues.

Limited use of +P should be ok, but I wouldn't recommend a steady diet. Maybe shoot enough to make sure they'll shoot reliably in your gun and that you can shoot them well, then every once in a while shoot a cylinder or two to keep up. Do the bulk of your shooting with standard pressure loads.