Ok, this is a bit complicated, but I'd REALLY appreciate feedback on doing this right away on my first run.
I want my stalker at the beginning, and I'm willing to pay (in raw mech tonnage) to have it.
My thoughts around doing this are as follows. The total tonnage of the "starter" unit is 190 tons (BJ,SHD,VND,SDR,LCT). I remember that back on the other forum someone had found the .JSON for the campaign settings. I figure I can change the starter mechs around a bit in one of a few ways and hopefully not break the game. The "starter" blackjack, used in the tutorial, most likely cannot be changed since there's scripted events that require it. On the other hand, I'm willing to bet that the "starter" is not the one you start mission #2 in. I'm willing to bet that for ease of coding, they just coded in a fresh BJ-1 without any special "ancestral" tags attached to it. Even if it DOES turn out to be a special spawn of BJ-1 with special flags attached to it, there's still several options available.
Make a save after tutorial.
If the BJ-1 you are given at start of mission #2 is NOT flagged special: Replace with STK-3F, and see if game breaks on mission #2 start.
If not, then go back in, and change the rest of the starter mechs to equal 190 tons (including the STK). make sure the stalker is set in the place of the locust, so that you do NOT bring it into mission #2 (making mission #2 significantly harder).
If the BJ-1 is indeed special, then see if you can change the rest of the unit around without breaking the game. Keep the tonnage at 190 including both the STK and BJ, and again keep the STK in the 5th mech slot so it stays on the leopard.
If touching any of the starter mechs actually piloted in mission #2 breaks the game, the at least try to code the STK into the slot occupied by the locust. This last option, while the LEAST desirable by FAR, should have the highest chance of working since the mech in that bay has absolutely nothing to do with mission #2, and therefore shouldn't even exist with unique item tags for it and it's components until the loading screen after mission #2. In this case, I guess I'm a straight up cheating bastard, because I will have my stalker, at the start of the game.
Please if any of the modders could assist me with feedback on how to make this happen I'd really appreciate it. I'd really like to be that guy that has one really huge mech, and a bunch of tiny lights. I think it would be fun to run mission #2 with at most a BJ and 3 lights, if not 4 light mechs. Consider it a challenge gate. If I can't beat it with like 75 tons less than I should have, then I don't get my mech.