so, I can set the gas cost specifically for my contract? I thought only the user can change the gas cost when he want to speed the transaction

yes

you can control the gas cost of your contract's functions by setting the gas cost of each operation in your code

but if I do it will be permanent. right?

yes, once you set the gas cost for an operation in your contract, it will be permanent and cannot be changed without modifying the contract code and deploying a new version of the contract.

thanks, need to read more about it

welcome