Yesterday this happened to me: I wanted to give a lvl 2 unit (lets say it's a Jax) its 3rd item which would be combined with the 3rd item already equipped. Now I had another lvl 2 Jax on the Bench, which, due to the time pressure, I gave the item, instead of the one being equipped already. Unfortunately I had another 2 lvl 1 Jax on my Bench, one being back from a shared draft round, so him having another item which I definitely don't want to combine with either of the other 2 items.
Now, assuming I have another Jax in my shop, is there any way I can control which item would combine with which, and which would be dropped off, through means like bench order or positions in the field or something like this? Or would it happen at random?