How would I make it so when a portal is opened, blocks begin forming around?

Ok, so... I'm trying to make it so if you open up a nether portal, the blocks around it will become infected kind of.

This means all dirt would slowly get more and more infected with netherrack until it became netherrack and as it spreads out, it'll also begin infecting more blocks with the nether, obsidian will not count as the portal will break and the portal would need to be active for the spread to continue.

Water will also not be affected as the nether infection I'm thinking of will only spread until it's too close to water.

But as time goes on and the nether infection spreads further, a new nylium will form from a mutation, due to the overworld affecting how it works, this would also come with more new blocks that don't infect mobs, the nether infection only infects certain mobs to be netherified.

Plants would be affected by this nether spread and be netherified once touched by the nether infection.

Idk what else to put here, but yeah that's about what I want to do with this.