Is it permissible for a storekeeper to take money allocated for hiring loading workers if he performs the loading himself and informs the entity that he hired workers?

You are not permitted to load goods and receive payment for them without your employer's permission, because an agent is a trustee, and he may not act without the authorization of his principal. The majority of jurists hold the view that it is not permissible for an agent to sell to himself, and leasing (ijarah) is analogous to selling in this regard.