For a quick answer, a slip on exhaust will not damage your motorcycle engine. The changes done by a slip-on are not big enough to cause any significant change in air flow.

Can exhaust cause engine problems?

If you have a problem with your exhaust, it will begin to affect the performance of your engine. You won't be able to accelerate as well or as quickly, and you won't get the same power when you do accelerate. This problem will continue to worsen if you do not address the exhaust leak.

Does damaged exhaust affect car performance?

Loss of Engine Performance -- If the pipes in the exhaust system become damaged or corroded, they can sometimes produce an exhaust leak that can cause the vehicle to experience performance issues, such as a decrease in power, acceleration, and fuel efficiency due to the loss of backpressure.