Ok, figured myself. And in case you wonder why I'm opening a new thread when finding things out myself? Simply because I already spend like two days searching for a solution, but obviously used the wrong search terms in Google and the forums. So in future, if you're bothered by continously repeated threads asking the same question (there were like 5 or 6 answering my question on this forum), then I'd recommend to improve the communication with your search function, as well as Google. I was searching for 'forge replacing vanilla ore', but the search term that brought all the happiness and answers was 'forge ore generation'. So it's nobodys fault here. I've had my fair share of effort, and I will every day when modding, so please, just answer questions, without acting all superior just because you know things that you learned from someone else knowing things, who learned things from someone knowing things.
If you have knowledge, share it! And share it in detail with useable code! The more infos you give, the less likely will people open new threads regarding the matter. That's how humanity works since more then 10.000 years...you gain knwoledge, you give it to others...WITHOUT all the drama involved when acting all superior... However, here's the solutions.
Code for replacing blocks that are not ore, needs to go in your EventHandler registered in your main file with...
Code to remove vanilla ore blocks because the upper version won't work on ore blocks (iron, gold, coal etc.), so you're allowed to distribute your own blocks via world generation...register as...