Replication still occurs to some degree in singleplayer, it’s a rather strange way of going about it as singleplayer(no dedi-one client) appears, to myself at least, to soft-launch a self-contained server within itself.
The problem could be though in the process of trying to dynamically alter the crate after it’s spawned… which when you think about it logically does not make sense. You would want the change to occur before the creation(as I presume it’s like everything else where it’s all done on construction) as, if you’re aware, when you approach the crate the items have already spawned inside as it’s not like a wheel of fortune type deal where it’s random upon accessing/“using” it.
Even further up than that however, is the fact that it may be the same deal with trying to modify resource requirements for crafting(which is not possible) where WC have stated that kind of information is stored at the class level(raw/absolute data basically) and the ability to modify classes does not exist in-game. At least yet, they may end up coming up with a way - how I wouldn’t have the slightest idea - with following the track with custom crafting recipes, there may be something there they can use to facilitate it.
Though, do remember to consider this is pure speculation on my part, I’m not too familiar with modifying existing game assets - I prefer to create my own things(to leave my stamp on them) and I believe there are too many people recreating the same things over and over to bother - so take what I say with a grain of salt in this particular topic anyway.