Quick tutorial for Sean Lang.
First of all, the starting 'Mechs are defined elsewhere, in one of the PAKs. When I was testing my mod I was using one of the Solo Missions and everything appeared to be working fine. Now I know that the starting Firestarter in the original campaign and the starting Centurion and Jagermech in the expansion will have the vanilla 35, 55 and 70 tons. I'll go looking for them later on, or someone else can make that fix.
In the mean time just sell and repurchase the starting 'Mechs and you'll find they have the corrected tonnage.
ANYWAY! For correcting 'Mechs all the changes you need to make are in MISSION.FST. Extract that and pick the 'Mech you want to alter. You'll find all the 'Mech files in data/missions/profiles.
For this example I'm going to be changing the Firestarter. The Firestarter is PM101xxx so make sure you open all the variants of the 'Mech you want to change.
Under [General] you'll find "f CurTonnage = x" where 'x' is the tonnage. In this case it reads 30. I want to change that to 35. Literally all you need to do is change the 'x' to the desired value and it'll change how much the 'Mech weighs.
HOWEVER, this creates some problems.
If you are increasing the tonnage then it is relatively simple. You've got an extra five tons so you can chose where to utilise the extra tonnage in that same file. Let's say I want an extra 3 tons of armor and 2 tons of ammo (just to keep things simple).
Scrolling further into the file I see [Armor]. "uc Type = x" and "f Tonnage = x" are the two variables in this section. Before you change armor understand that Armor Tonnage and Armor Points are two different things AND are independent of each other.
The former affects how much space a 'Mech has when you are fitting guns to it. If you set it to 100 tons you'll find that you can't add any guns BUT the 'Mech will be no stronger than it was before.
The latter is the actual protection of a 'Mech. You can have a 'Mech with 1 ton of armor giving it loads of space for guns but 1000s of armor points making it nearly invulnerable.
Just because all that is complicated enough, the amount of Armor Points appears to be a multiplier on the Armor Tonnage which I'll explain below.
If your 'Mech has 1 ton of Armor, that gives you 16 Armor Points to spend. If you exceed that, you'll find that the game reads the 'Mech as having more than 1 ton of armor. So referring to our above example, if I try to add three tons of armor but add more than 48 armor points, I'll find that if I remove two tons of weaponry, I won't be able to add them back because the game thinks there are only 1.9314etc tons available.
Here is where "uc Type = x" comes in as well. A type of 0 is Ferro-Fibrous Armor. A type of 1 is standard armor. In MechCommander Ferro-Fibrous Armor gives you a 1.25 modifier to the amount of Armor Points you have available to spend in the 'Mech's .FIT file. So if I want to add 3 tons of armor, I have an extra 60 points to spend, not 48 points as mentioned above.
In other words, modify with care.
Trying to reduce a 'Mech's overall tonnage is more difficult. Presumably you want to balance the loss of both armor and guns, not just x tons of armor with the same guns, or vice versa. You have to remember to calculate how many armor points you need to remove for each ton of armor you are removing, and don't forget to consider armor type.
AND REMEMBER TO DO THIS ON ALL VARIANTS, NOT JUST -A.
Hope this helps.
Just make sure you do some thorough testing. You'll probably find that on many 'Mechs the existing don't fully matchup so you'll need to remove one or two more armor points than you thought. Just subtract a couple at a time until it works.
You don't need to reboot the game each time, just return to the main menu and it will reload the .FIT files.
