well i have seen some 24v 10A relays being used for 60V 4A operations and they have been going good for over 4 months now but then I'm quite skeptical about the whole idea.
And it might last for the life of the relay. It relates to how often the contacts are commanded to open and close, whether the contacts are sealed or open to atmospheric contaminants, etc, etc.
Specs are specs, and good engineering practice is to not exceed manufactures ratings and more often are over speced, that is buying 10 amp rated contacts and only using them at 5 amps in the actual application. It's considered a poor practice to utilize components at there maximum ratings.
Lefty