What happens if I don't increase the electrode gap?

Misfire. Check Engine light. Loss of power. Loss of fuel economy.

These spark plugs may be used in a variety of different engines from different manufacturers. The spark plug manufacturer uses a best guess when they set the gap at the factory. However the factory engineers who designed your engine determined from lots of testing that 1.3 mm works best in this engine.

Ask yourself these questions. Is your engineering degree better than the engineering degrees of the Ford Engineers who designed your engine? Have you placed your car on a chassis dynomometer to see which combinations give better performance or fuel economy>

Gapping the spark plugs correctly is even easier than replacing them. Do it right or do not do it at all.

Non-standard spark plug gaps will cause the ignition coil or coils to eventually overheat and fail.

Diminished spark, incomplete combustion, poor performance, slow deterioration of the catalytic converter from incomplete combustion, etc.

BTW, why would you want to do this?

.95 x 39.37 = .037 inch

1.3 x 39.37 = .051 inch

Just do it.