Oh ok I remember it, but yeah, as you said, you can't just change the €14.99 like you can change the 100 gems, because as you said, there are multiple checks (google play is involved here, and their protection is ways harder to bypass lol).
You have multiple options for what you want to do:
1- buy a dragonhunter and edit its rarity. (what you wanted to do)
2- change the flag of the purchase currency (if it exists here). (what I told you about in ly last post)
3- buy a random legendary heroe and edit something to get the dragonhunter instead at the sale rarity (maybe there is a flag for each heroe, or an ID). The advantage here is that if there is an ID involved (usually some random numbers stacked in about 10 Dwords), it is easier to spot than a simple rarity flag (usually 1 Dword).
4- hack the shop. (see below)
What I mean by that is the kind of thing Nofear did in the game "last day on earth". He first searched for the price (real money, as a "double") of an IAP he wanted to get.
From there he managed to get the pointer to the ID corresponding to the content of the IAP (he copied it). He then did the same thing with a non-IAP purchase to get to the pointer of its content's ID. He finally replaced this last pointer by the first one from the IAP.
This method is basically an ID tweak between contents of 2 purchases. After that, he could get the content of the IAP by buying with just in-game money the other purchase.