>= Gen 6, you're supposed to be using EC. PID is for Gen 3 - Gen 5. My bad.
Once PKHeX supports transfers, if you engage PKHeX in hax mode, you should be able to drag that file into another PKHeX window with a Gen 7 save loaded.
Over there, you can change the met details.
Finally, change the EC.
(Note: New EC = Original EC xor 0xFFFFFFFF)
Alternatively you can modify a Gen 3 Spinda (in SM/USUM presumably. maybe get one from the encounter database), then give it the New EC.