Let's see...
You didn't download anything from an illegal source.
You didn't circumvent any mesure of copy protection (an option written in plain text is not copy protection).
So no, what you did was not theft. It was EA beeing stupid. Sure, they want you to pay 10$ for the DLC, but they don't actually make sure in any way, that you have to. They hand it to you and basically hope that you are kind or stupid enough to actually pay. I don't know how the laws are in your country, but where I live, none of what you did is illegal.
Having options hidden in a .ini file is common practice with PC Games, Players as well as Developers know that. As a player, if you find an option in a .ini, you can assume that you can alter it.
You didn't download anything from an illegal source.
You didn't circumvent any mesure of copy protection (an option written in plain text is not copy protection).
So no, what you did was not theft. It was EA beeing stupid. Sure, they want you to pay 10$ for the DLC, but they don't actually make sure in any way, that you have to. They hand it to you and basically hope that you are kind or stupid enough to actually pay. I don't know how the laws are in your country, but where I live, none of what you did is illegal.
Having options hidden in a .ini file is common practice with PC Games, Players as well as Developers know that. As a player, if you find an option in a .ini, you can assume that you can alter it.