Modifications, unless they can definitively be attributed to a specific failure can NOT void your warranty. Scare tactics are employed by some dealerships and service departments to sell services; everything from oil changes to add-on parts. Many service departments rely on ignorance and the sale of "Genuine" parts to keep them in business.
The Magnuson–Moss Warranty Act protects
consumers and a good working knowledge of it will shut down most if not all dealership objections. If not, find another service department.
Forgot the FTC link
here
Now if you install a 100# shot and snap a crank, good chance they will connect the dots and tell you to pack sand; a cat-back exhaust... no friggin way.
/r
Allen