Is it possible to modify these pokemons using power save?

[Shev]

the event zapdos with HA, shiny xerneas and yveltal from the event.....is it possible to make them 6ivs, right nature w/o having problems in competitive?

[Excalibur0126]

It should be possible as the IVs and nature is randomized.

[Black117]

Its is possible to modify any event Pokemon using Pkhex and Powersaves though people now tend to use Pkhex to avoid the bans from Battle Spot or GTS. Powersaves is fine and all to change the Pokemon's ivs to a max of 31, though I don't think it changes the PID as well which is basically another identification code for any Pokemon. That said, I not sure about using Powersaves to mod for ivs since there's a stronger likelihood of People getting caught. Just recently in a Japan Cup qualifiers in VGC, some players got banned for using powersaved files and data. Basically straight out the ordinary stuff like x999 items and all. Personally I don't recommend using hacks due to the potential to get caught/exposed, but if the ethics don't bother you then do as you wish.

Again I'm not supporting either side, but I'm letting you know the hack checks are getting more I guess "better" with people using the seemingly mandatory legends.