I know this topic has brought up a couple of times, but I did my research and tried everything I could.
I did not want to necro this thread, but here it is, because I also tried to make a mod:
https://steamhost.cn/steamcommunity_com/app/1213210/discussions/0/598514011709977559/
I also refered to this guide:
https://forums.ea.com/discussions/command-and-conquer-franchise-en/re-how-to-get-rules-ini-working-in-cc-red-alert-remastered/7306270

Tools I used:
XCC Mixer
Mix Editor
Mobius Map Editor

Here is what I want to change:
[Easy]
Firepower=1.2
Groundspeed=1.2
Airspeed=1.2
BuildTime=.8
Armor=1.2
ROF=.8
Cost=1.0
RepairDelay=.001
BuildDelay=.001
DestroyWalls=yes
ContentScan=yes

So in the campaign for exampe, I want to change the cost to default on easy.

These things I tried:

I put the rules.ini in the main folder
Not working.

I extracted the rules.ini from local.mix, changed it and put the altered rules.ini back into the local.mix
Not working.

I made a mod with the correct mod structure, so in C:\Users\*\Documents\CnCRemastered\Mods\Red_Alert\RulesMod is a json with this in it:
{
"name": "My rules mod",
"description": "change the ini",
"author": "Spooky",
"load_order": 1,
"version_high": 1,
"version_low": 0,
"game_type": "RA"
}
And in this directory is a folder named ccdata with the rules.ini in it. I activated the mod.
Not working

I checked the campaign maps directly from the mix files, if they overwrite the cost within their own rules.ini logic.
The don't.

What am I missing?