Upgrading Green Items?

Can anyone tell me what happens if u upgrade a Green item?

I have, for instance, Rotscales Recurve Bow. It's a 'Poisonous' prefix Bow, if you didn't know, with great stats-

Health
33% Poison Duration (that's the prefix)
+5 Energy (or is it 10?)

The point is, I also have a Sundering Bowstring (20% armor penetration) that I would put on if I knew all that would happen is that the Poison Duration stat gets replaced. But I'm wondering if it might replace other stats too.

Any ideas what happens to a Green when u Upgrade? Thanks in advance.

You can't upgrade a green item, period.

You can NOT upgrade a green. period

edit: you beat me to it

Ah well then that certainly makes things simple! Thanks.

actually you can, customize it and give it an extra 20% damage