How do I make stacks of objects default to "Add New Stack"

[Duggan]

I'm having difficulty figuring out where in the code this is defined, but if you set up an item, such as a piece of gear, with a quantity in a stack, it defaults to choosing to add individual items. I would prefer for the behavior to be merging to the existing stack so that, if a player buys 4 orders of Boomex (which come in 5 each), they wind up with "Boomex (x20)" instead of 20 entries of Boomex. I can see the other parts of this in the BuyCash entry, but not that menu.

Semi-related, if I wanted to switch from characters buying their gear from a personal supply of money, and instead change it so that they accumulate a "cost" for their current gear (so instead of someone starting off with $100 and paying $15 for a rifle and $3 for 5 doses of Boomex, and having $92 left, I instead want to simply note that the "cost" is $18). The reasoning for it is that, in the Planet Mercenary system, the money is owned by the company, not by the mercenaries, so it doesn't make as much sense for them to have "cash" on individual characters (eventually, I plan to create a new "Company" type that can "own" individual mercenaries and deduct their "cost" from its money, but for now, it's just handy knowing how many resources a given mercenary is costing their company).