In most cases, no. As long as your new exhaust doesn’t damage any other parts of your car then the warranty on your vehicle should still be valid. For most types of car warranty, it will remain intact after you have fitted a new exhaust. There can be some exceptions to this rule - for example, if the new exhaust has caused damage to other parts of the car that then needs to be repaired. This probably won’t be covered by your warranty but in most cases, you will be fine.