Make a block corrupt others

hello, im very new to using MCreate and ive figured out a lil bit on my own already but the problem im having boggles my mind still, so basically, im making a mod about parasitic mold that corrupts nearby blocks into their "moldy" version so to say so that it can spread out to let its mobs spawn in more areas (vanilla mobs can also get infected but thats a problem for another day) the main issue is i dont know how to make the block basically take over the other ones around it, is that even possible? if so how?