Hello,
Modifying a price is possible since you have various triggers in HikaSerial and HikaShop.
But the real problem I see is regarding the payment platform ; because if you want to change the recurring price, it means that the payment plugin would be able to accept a modification in the reccuring 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.