In your "...\Documents\My Games\XCOM Chimera Squad\XComGame\Config\" folder there are a bunch of '.ini' files that hold simple values for things in game that can be changed to tweak things to your liking.

For example, in 'XComStrategyTuning.ini' you'll find the line:
FieldTeamRankCost_Intel[2]=120
Which sets the initial cost of a rank 3 field upgrade.

Slowing down assembly(research) times is definitely also possible this way. I'm not sure if you can modify difficulty scaling in the way you want or not, you'll have to look around.

I too am looking to make minor tweaks. Although I figured out how to modify some abilities, I cannot locate the folder to modify breach abilities or how to add a few charges to some skills. For example, how do I increase the damage of Slam? Better yet, how do I make this ability usable in combat and not just in breach mode?

Basic value changes, like the costs of things, or damages/cooldowns can be altered in the ini files mentioned previously. Specifically for ability damage, you're looking for: 'XComGameData_SoldierSkills.ini'

You probably can't make breach abilities available in regular combat without editing the game's script files. Which you need to download the SDK for, and have (or being willing to learn) some basic programming skills. The game is built off the same scripts as XCom2, and more generally 'Unreal Script' because it's built with the unreal engine, if you're looking for tutorials.