Of course you can, if I understand what you're asking correctly! You can only do this for singular mesh files though, not objects put together to form new objects or something like that.
Just go into your Feralheart folder and open up items.cfg with Notepad or a similar program. Go towards the end of it and copy one of the item codes and paste it.
Change the name that is in the [ ] to whatever you want it to be called. Change the mesh that is after mesh= to whatever mesh you want it to be. Change material= to the name of the material. (If that isn't there, add material= under mesh=.
I don't know how to make items using the codes and stuff below that, so you'll have to find another tutorial on that.
(Sorry that it says Oak Tree, I changed it halfway through)
This was a bit rushed, so sorry that it doesn't make sense! I can provide a more detailed tutorial if you want.