part time work when near retirement

An employee in Belgium, when nearing retirement age, can opt to work part-time (with agreement of employer) and the government will contribute an additional monthly amount to the part-time salary. Whether the employee can take on another part-time job or work as an independent as well is questionable, but HR are not giving a consistent and detailed answer. The same for whether one can join the govt contribution system after working part-time for a while, or whether one can join it and then withdraw and stay as a simple part-time worker in order to have another job. After wasting much time googling, perhaps someone can direct me to a particular website, or maybe know how the system works. The alternative would be a brief consultation with a specialized lawyer if you can recommend one. Many thanks.