Is it permissible for one beneficiary of an endowed waqf to relinquish his share to another beneficiary?

It is permissible for a designated beneficiary to relinquish their share of the endowment's proceeds, because they own it in full and can dispose of it as they wish. They may sell it, gift it, and it can be inherited from them. As for endowments designated for a general charitable cause, such as the poor, the beneficiary only owns the right of usufruct (beneficial use), and is not entitled to lend or lease it. The matter in this case reverts to the endowment's supervisor.