As in, what say... the chest in the demon door in the guild has inside it? if so, yes, I've been trying to get specific items to spawn for a while (finally succeeded last night actually), and that was a possibility I explored when my chest spawning wasn't working right.
EDIT: If that is what you're looking for, it's a very similar method to the chest spawning, you just edit the existing chest in the same way you would the chest you're trying to spawn. If you want I can grab a few screenshots of using Albion Explorer to edit a chest's contents, or you can just look at the chest spawning guide
Ah. Of course, there's the FE + Freeroam method on it's own, which I normally use (simply text editor ^_^) but AE is best for seeing where it goes before you start the game. If you're just editing the chest's contents you can get the TNG out with Freeroam and edit it that way, but as JohnDoe said, the guides are useful ^_^