Could other third-party hardware replacement parts be used for or in conjunction with the Dell Laptop within and outside the warranty period?

During the warranty and support period you must not make any modifications on the device / laptop, this will void the warranty and the device won't be eligible for future repairs. 

However, we have a list of tested third party external hardware that can be used in conjuction with your laptop, such as stylus pen, protective sleeves, and couple of other accessories.

After the warranty expires, and you own the device, you are in control of the service and support.