Typically hard drive, memory and mini-pci bays are accessible by users and replacing the parts in them will not void the warranty. It's only when the whole chassis is dismantled that the warranty is affected. That is why you see a "Warranty Void if removed" sticker seal on one of the chassis hole covers on many laptops. However, you should read the fine-print in the warranty paperwork that comes with the laptop to make sure that replacing any of these parts doesn't void the warranty.