Replace coal ore with a custom block

Hi, i'm creating a compact coal's ore and i want to replace the already existing coal's ore with my new brand block. I DONT WANT to put my new block in stone i just need to replace 1 or 2 block of default coal's ore into my ore in the same vein of coal. 

How can i do? 

I have the 1.8.3 version of mcreator and i 've just tried to put coal's ore instead of stone in the "blocks this ore can replace " and frequency on chuncks -> 20  and frequency on specific chunck ->17 but it still doesnt work. 

P.S I selected the surface dimension  to generate it. 

Thx a lot for answers :)