Texas (under 29.02 of Penal Code) recognizes robbery and aggravated robbery as a charge. Thus, if you are asking can aggravated robbery be reduced to simple robbery, then that is work for the accused's lawyer. Sometimes D.A.'s offer time on a reduced charge... but not likely if the D.A has a strong case. You have given some very detailed facts on this public forum which is not good. The best advice I can give is to not do this. These are facts that should be discussed only with an accused's lawyer.
The information provided is not advice but a legal perspective and you should schedule a consultation with the lawyer of your choice.
these facts sound very bad since someone was beaten with the gun - it is possible for there to be a reduction in charges but you need a good lawyer to speak on your behalf. In Dallas I suggest Carl David Ceder.