Hello,
HikaSubscription is not using that kind of "recurring" API where it requires to create the plan on the payment platform too.
Maybe one day, but that's a not in our plans since these API are sending the plan & subscriptions into the payment processor and not your store.
Thus, it's not possible to change the price of a subscription while it's on auto-renewal ; you need to cancel the auto renew and let the customer perform the renewal manually, with the new price.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.