Is it permissible to collect the deducted amount from one's salary from the company through other means, such as fictitious overtime hours, especially since the employment contract has not changed?

It is not permissible to take money from the company covertly as compensation for a salary reduction, because what is considered is what has been agreed upon. Even if the questioner has a right, it is not permissible to take it through lying and betrayal, for the Prophet, peace and blessings be upon him, said: "Render back the trust to the one who entrusted you, and do not betray the one who betrayed you." Sheikh Al-Islam Ibn Taymiyyah mentioned that among the forbidden deceptions is for a person to take his right through betrayal, such as one who embezzles from his employer's money under the pretext that he is taking his full right. This is forbidden because he is lying about his entitlement to more than what was stipulated.