PKHeX is open source. You can download the repository at any arbitrary commit and rebuild it yourself.
If it's an issue of getting an old plug-in to work, it's better to just get the plug-in updated.
I did check Sky Temple to see if it was possible without editing after when my friend explained it to me. I do know I COULD edit it to do this but I wanted it to be an authentic run.
Thank you nonetheless for taking the time to tell me I think I will play it without.