Quick and dirty mod to add the ability to customize certain items/entities with JSON via the mod settings.
Supports:
- Setting underground belt length of arbitrary belts and pipe-to-ground / underground pipes
- Adjusting the research cost formula of infinite / formulaic upgrade research
- Adjusting the product count of specific recipes
- Adjusting the ingredient count of specific ingredients in specific recipes
- Adjusting the stack size of specific items

Sample JSON to exhibit syntax:

{
    "underground-belts": {
        "_comment": "Entity ID, sets underground distance of belt",
        "express-underground-belt": 12
    },
    "underground-pipes": {
        "_comment": "Entity ID, sets underground distance property of fluid box",
        "pipe-to-ground": 19
    },
    "tech-formula-cost": {
        "_comment": "Technology ID, sets formula",
        "artillery-shell-range-1": "1.2^L"
    },
    "stack-size": {
        "_comment": "Item ID, sets stack size",
        "iron-plate": 2000
    },
    "result-count": {
        "_comment": "Recipe ID, sets result count",
        "copper-plate": 2
    },
    "ingredient-count": {
        "_comment": "Recipe ID to modify",
        "copper-plate": {
            "_comment": "Item ID - sets required count of ingredient matching Item ID",
            "copper-ore": 2
        }
    }
}

Different category (belt length, research cost, etc) objects may be empty or excluded if unused.

Minimal, useless config:

{}

I recommend using JSONLint to validate / format / compress JSON.
https://jsonlint.com/

Intended for private use, but use it if you want I guess.