Would do little.
The most the UNSC might be able to manage is to increase the size of their Spartan program. The fact is that technological innovation is expensive. And the UNSC would really not have any idea of where to begin, unless you revealed all the abilities of the Covenant. In that case, they could redesign their ship, their defenses, and battle doctrines to try and compensate, but that might only buy them a few more decades. And since the only reason why they survived was out of sheer good timing and a little bit of luck, you might actually end up dooming them.
Worse, they might try and seek out Forerunner technology and accidentally earn the attention of the Covenant sooner.