I just want to know,can I use the EVGA gtx 980ti hybrid fan cooling kit with the g1 gaming 980 ti?I highly doubt it since it has it's own custom pcb design but I just wanted to know,and if I can,will I have better temps and wil there be more sound?
No, you can't. Only reference designed 980 TI is compatible with that Hybrid Fan cooling Kit.
See - http://www.evga.com/Products/Product.aspx?pn=400-HY-0996-B1 .
Anyway G1 Gaming 980 TI cooling is more than sufficient/quiet, i see no reason to replace it.