A guy I work with wants to try out the vita play with the ps4. Does he have to be at my house? If i do this can he make changes etc to the system or account?

Yes he has to be at your house. Both systems need to be on the same network.

I don't have a Vita, but I believe the PS4 and Vita have to be paired together, and they more than likely have to have the same account on both. So you'd have to let him add his account to your PS4. In fact, doing that would prevent him from making changes to your account at all.

It's recommended but not required that they be on the same network (for latency etc.), but if you have fast enough connections, it will work anywhere.

http://www.extremetech.com/gaming/17...er-connections

Good advice here. I think your PS4 would have to be his PSN account's "home" PS4, and what I don't know is whether a PS4 can be multiple users' primary system. I'm pretty sure it can.

Alternatively, he could remove his profile from his Vita and make it yours, but that would require your login info.

Either way, he'd be able to turn your PS4 on remotely, which could be annoying.