Firstly, governments do not have rights. Rights are the purview of individuals. In the US, at least until recently, government derived its power by the consent of the governed, but this should not be understood that individuals ever ceded rights to the government -- rights, by definition, are intrinsic to an individual by virtue of existence, and cannot be altered or taken away by government. Secondly, the proper role of government is to safeguard individual rights. Your question may be more properly stated as "Does the government have the power to institute a draft?" Certainly in the US it has done so in times past, beginning with the North - South conflict in the 1860's. Establishment of a draft then resulted in riots in NYC that left many dead. Although acts have been passed to institute a draft, its Constitutionality has been questioned several times, because it allows the power of the state to coerce an individual into the military. Amendment 13 forbids involuntary servitude, and was made part of the Constitution as the final remedy to any kind of slavery in the US. During the Vietnam Conflict, this amendment had been used once again to argue that the draft is a form of involuntary servitude, and apparently draftees who argued that their sovereign individual rights had been violated by being drafted were either released from or were not forced to join the armed forces.
I would add that this is rooted in the preamble to the Constitution which states that one of the reasons for the creation of the constitution is to "provide for the common defense." Since the individual states were not strong enough to withstand an attack from a foreign power, and since the states might not be all that interested in helping each other, the power to protect was designated to the Federal government. It is generally believed that in order to fulfill this responsibility, the government has the power to draft in a time of war.
Yes- The Conscription (military draft) can be opened by the government with no problem and at any time. Men are always asked to join the Selective Service at the time they register to vote and in many other ocasions, and this is basically a way to put them on a database to pull their names out in case it is neccesary to call a draft. As far as democratic core values, all I can come up with two government proposals which could become regulations that enable this to happen: The HR163 proposal (Universal National Service Act of 2003) calls for a national draft and Bush's Executive Order No.13223 which called for the National guard and reserve troops to be activated immediately and some to be drafted in case of terrorist attacks. Jimmy Carter is known to have activated the draft and, as you know, it was fully activated during Viet Nam. The importance of knowing these executive proposals and orders is that, once you create one, you can amend them and turn them into bills and laws (with the proper procedures) and yes indeed the draft could be re-instituted any time.mandatory draft.