Changes don't apply on the save file

[Bepposan]

I've tried to find solutions for hours, I just installed PKHeX and I'm trying to mainly modify the nature and the cosmetic tab (height and weight) of some of my pokemons. For the cosmetic tab it says illegal so I guess there should be some sort of proportions to keep, but that's not the problem i can keep it that way, I don't understand why, even if PKHeX says legal, the nature doesn't change. 

I use Riunjinx and I have a save folder with two other ones (0 and 1) in it, there is also a dotlock file, an extradata0 and an extradata1. When i overwrite the main file in one or both the folders it just goes well but when I open the game or PKHeX again it just shows the save before the changes.

If someone could help me I would be very grateful.

Forgot to say I'm playing Pokemon Legends Arceus

Edited March 3 by Bepposan

[Kaphotics]

When you are done editing a Pokémon, you set it back to the save file in whatever slot you choose.

When you are done editing a save file, you export the save file.

When you want to use an edited save file, you import it back to your console and overwrite the existing save file so that when the game boots up, it reads the edited save file.

[Bepposan]

I tried to change the nature of a pokemon and what I did after is Export SAV. I overwrote the main file but it doesn't work.

Even if i have the changed pokemon in front of me and if I just move myself to a different one, the changes that i made on the first pokemon just disappear. 

Even if I save them one by one, when i re-open the file or switch to a different pokemon it simply didn't save anything.

[Kaphotics]

Data doesn't magically revert. Re-read my first message, and try importing your save file to your console first to ensure you are doing things correctly before you try again with an emulator.

[Bepposan]

I re-opened the save to check if it was all right then again i tried to do some changes but nothing when I export the save the changes just don't apply.

[apocalips]

Did you drag the edited pokemon to a slot (or set it in a slot) after editing?

[Bepposan]

Ohhh now I understood where i was wrong, basically I didn't see that I had to copy the edited pokemon on another slot, surely a stupid mistake by me.

Thank you for your time guys and for helping this newbie out, I'll surely use this program from now on.