Legality of changing only one aspect of a legit caught pokemon

[Xenaer12]

Hi, just want to be clear about two things.

1. ONLY concerning Gen 5-7 ( gen 3 and 4 i know are a bit more complicated ), will ONLY changing the nature of a legit caught shiny Bagon for example still be legit or will it be necessary to reroll the PID of the pokemon? And what about other variables such as IV, gender etc ?

2. And in what generation did IV's stop being linked to nature etc ?
 

I know it might have been asked before, but everywhere I try and research people have conflicting ideas. Thank you

[Guest]

Any modifications render a Pokémon illegit.

IVs got decoupled from PID/Nature in Gen. 5, and Gender then became decoupled from PID in Gen. 6.