No, an executor or administrator has no right to remove any beneficiaries or alter any of their shares. Only the testator has the right to make any changes in his/her will. If there's no will, beneficiaries entitled to a deceased's share is determined by the intestacy law.
Read more: What Happens To My Stuff When I Die? (Singapore Edition), Guide To Making a Will (Singapore Edition), All About Probate & Administration (Singapore Edition)