Changing the force field parameters is not a good/recommended approach. This is due to the high number of parameters you have to know. Many of them, you cannot obtain from experimental data. Instead, you will need high precision methods like Density Functional Theory, Hartree-Fock, pos Hartree-Fock or semi-empirical methods to calculate them for two, three ...
You need to use the advanced option --score_only which means:
score only - search space can be omitted
To get info about advanced options you run vina --help_advanced that will return:
--receptor arg rigid part of the receptor (PDBQT)
--flex arg flexible side chains, if any (PDBQT)
--ligand arg ...