Is it permissible for employees to sign a clearance absolving the employer from any claims to end-of-service benefits, given that the salary in the contract is divided into a portion for salary and a portion calculated from end-of-service benefits, and the employer's desire to apply the Islamic ruling?

It operates according to labor law unless there is an explicit agreement that contradicts it, for the law is akin to custom and tradition. If an agreement is made with the employer that a portion of the salary constitutes end-of-service benefits, then this agreement overrides the application of the law, because "the contract is the law of the contracting parties," and it must be fulfilled, based on the words of Allah Almighty: (O YOU WHO HAVE BELIEVED, FULFILL [YOUR] CONTRACTS), and the words of the Prophet, peace and blessings be upon him: (MUSLIMS ARE BOUND BY THEIR CONDITIONS). Thus, custom is considered in the absence of an explicit statement to the contrary. However, if there is an explicit statement contrary to labor law or company customs, then the explicit agreement takes precedence. Ignorance of the law and your previous consent to the agreement do not have an effect.