Not a service manager or anything, but read the fine print on the warranty. Of course they can do that. Warranties are just like insurance, if they have a way to get out of paying for something, they will. How can they guarantee their product will work when you have modified/changed and your modifications could be the reason for it breaking or having issues requiring service work? They can always say your mods are what caused the problems and there is no way for you to prove they didn't. Usually ANY product you buy has clauses in the warranty that if you open the housing or modify it in any way the warranty is voided unless the work is done by an authorized dealer/agent of the company.