Yes i have been using JDM Alto on normal fuel since the beginning. My car was a 5 grade 5200km driven import so basically brand new and current odometer reading is 60,000km and normal fuel has been used.
All you need to make sure is that you get fuel from a good reputable pump.
As for the de-tuning the PKDM Alto i think they might have done slight tweaks but not so much k 39HP ho gaye
One think i know is that local mein Copper plugs hain as compared to iridium in JDM. Spark plugs wont make a great difference lekin aisi choti choti cheezain maybe tweak ki hoon.
Performance difference feel hota hai in AGS and it feels lower than JDM but thats due to AGS trans and not the engine. I am pretty sure that if you race a manual VXR alto and JDM alto the VXR would win way easily
I did race my 8th Gen when almost brand new with a 80,000km driven manual 7th gen and i lost obviously and yes my car was originally 5200km driven, i verified the auction sheet myself.
End point i dont think local alto is 39HP. Max 2-5 HP ka difference ho sakta hai in Local. Major slowness in PKDM is due to AGS trans.