If it helps, I'm FrankenPre'ing now and had the same question. Just got to the same point and noticed that below the shield (thin metal plate) where the antenna wires go into the commboard, the wires have a pin/plug.
I (very carefully!) pried back the shielding to expose the pins and disconnect the antenna wires at the board. Can then remove just the board, put in the new one, and carefully reconnect the pins and close the shield back down.
I'm giving it a go this way so as to keep the new bezel/speaker/headphone jack, too. Especially after noticing how hard it is to remove any of those things individually.
However, I'm also 1) a noob at this so maybe this isn't great advice. and 2) I'm using a VZW Pre 2 for my build and noticed the antenna structure, etc, all looks the same as my Sprint Minus. Dunno if that's so with the unlocked.
I'll post back how it goes later.