Hello!  Based on Consumer systems, you can 'upgrade' or replace whatever component you wish in the computers, as long as you do not damage the Dell supplied components.  So if you upgrade the HDD's to SSD's you should be fine warranty wise.  The problem you may encounter is if you need warranty work done on the unit, you may have to replace the HDD back into the machine having issues as Dell may need the parts for one thing or another.  
Hello everyone, I currently work for a business that is in the middle of making some IT decisions with costs in mind. With this said, there is a suggestion on the table with purchasing Dell computer equipment w/ the 3 year warranty, but upgrading the hard drives in those Dell computers to SSD's from another vendor, as the SSD hard drive is beneficial for performance for our programmers, and we can save a good amount of money by going to another vendor instead of upgrading through Dell. With this said, by upgrading the hard drives to SSD drives purchased by another vendor, will the other Dell components (LCD, motherboard, etc.) with the exception of the hard drive not be covered by the 3 year warranty purchased? In other words, since the SSD purchased from a different vendor is not covered by Dell, will the other Dell hardware components still be covered? I need a response ASAP. Thank you.
Warranty question