You could make the blueprint with the instances in the blueprint, then place dummy boxes or whatever you like in the level at the locations you want your barrels to be in, and just copy-paste the locations of them in to the locations of the instances in the blueprint.
What on earth are you talking about? Is this gibberish? Are you some sort of bot? Just… what?!
By the way, you can use Foliage tool(Shift+4) for that purpose. It’s not strictly for vegetation only. After placement you can switch to Select mode(small arrow in left pane) to tinker it further after “painting”