There are two options you have

1. use BepinEx and the "Swap Characters" feature to do it whenever you want, though doing it that way can make it more likely to break.

2. The recommended way is to use the MadCard editor by DarkSignal, which you can find in the modding resources for MPN. You can create story missions with the characters that can override the main story missions.

how to edit them in myself ?

Ah thank you, for some reason I didn't think it was connected to the HUD so I kept pulling my hair out trying to hide it

In the settings there's an option to turn off the UI, it also makes the line disappear.

Isn't the orange aim-line the Aim Assist skill in Arena mode?