system
Given the following post, respond as if you're commenting on Reddit:
human
[Deathnote] Can a user prolong his or her life by writing a death for themselves to occur significantly into the future?
gpt
No. You cannot extend a person's original time of death. What will happen is that the cause of death you put wouldn't be physically possible to achieve, and will cause the death to default to a heart attack/or you will simply die of whatever cause written in the note at your original time of death. 

However, if you kill someone that will in the future do something that shortens your life span, (Killing someone that plans on killing you in the future for example.) killing them will extend your lifespan. But there's no way to know since you can't see into the future or see your own time of death. Also, killing someone can do the opposite, and cause you to die at a sooner rate in the future. (For example, killing an important family member that would have taken you to the hospital for a disease you will have in the future.) 

Killing someone with a death note won't cause their death to directly cause death to another person though, just changing the future's of affected people in a way that may increase or decrease their lifespans.