Changing a cookie and changing its lifetime?

Question

HTML

Tell me, did someone come across with the substitution of cookies and changing their lifespan?
How realistic and possible is this?

Answer 1

There is a plugin for firefox. Perhaps not anymore. Google it

Answer 2

It's fantastic. Don't trust anyone.

Answer 3

the server will overwrite immediately,
and if the time is also sewn into the cookie, it will also mark it as a cheater