Yep it's definitely in the files somewhere. Unfortunately I cannot remember WHERE in the files it is... CEF file probably (forget what the real name is - try searching it here on the forums). If I recall there is a rewards section that gives rewards (aka guns) based on the number of towers liberated. Sorry I'm not being more helpful, but it's been a lonnnnggg time since I touched those files...
PS - Pretty sure there is also a random xml that pops up notifications when you unlock guns so that would need to be changed as well.
And all this science, I don't understand... It's just my job, five days a week
I did notice a bunch of stuff in the shop file regarding tower unlocks and mission unlocks, and I believe that the mission unlocks would be handled in the open world mod. However, I also noticed that the Open world mod, the open world immersive mod and the attachments mod have no shop file in them.
I compared the clean copy of the CEF file with the open world copy of the CEF file (the Nompare plugin in Notepad++ is such a useful thing...), and noticed a few things:
The Signature Weapon unlocks list. It's the only series of numbers with odd numbers like 17, or 23, on it.
The skills unlock list. I assume the list I found was the skills unlock list, because there were 12 of those changes listed almost sequentially. The number of locked skills in the vanilla game is also 12.
A series of 6 changes, whose purpose is unknown to me as of now.
So, I'm stumped about where the unlocks weapon unlocks and the attachment unlocks are stored. Maybe I'm missing something.
P. S. There do exist a bunch of ark FCBs regarding weapons in the entityarchetypeslibrary folder in the Open World mod, some of which describe weapons (cross-referred this data from Janne's FC4 archetype browser, thanks to them.), but I haven't explored them yet. Maybe they hold the answer to this conundrum.