How does purification work?

Hello, so for the game I'm making - I wanted a theme of the game to be caring for certain Pokemon, and I think using Shadow Pokemon might actually fit the bill really well - though there doesn't seem to be a lot of info on the pokemon wiki about how exactly purification works.

Mainly I'd like to know if I can alter the script to have purified Pokemon counted as "special" so they can't be released and if possible given a diffrent form upon purification.

Like for example - the shadow Pokemon is really angry, dark, and kind of edgy - but the "purified form" would just be really happy and excited compared to its standard form. So that the player can tell which Pokemon was a shadow at some point and they'd have something special to get out of purifying pokes.

So I guess anyone know how feasible this idea is and how I can learn more about altering the purification stuff?

Edit:
I was testing the items list out that's on the wiki, and I don't know if its due to the update since it was before my time - but none of them seem to work if you don't put the plural form in the pbs item file. You'll instead get a message that the text isn't a positive integer.

Feel like that might need to be updated on the wiki.