Nonsense. Federal property and troops were absolutely federal BEFORE secession, and ANY acts of force against them by definition were "rebellion," "insurrection" and/or "domestic violence." After secession, those properties and troops would no more automatically belong to Southern states than would, for example property owned by a citizen of France.
Federal efforts to reinforce those forts might be problematic, but nearly all had no troops to speak of, and no federal reinforcements were sent by President Buchanan. So their illegal possession by Southern forces constitutes "rebellion," "insurrection" or "domestic violence."
By the way, to my knowledge there were no Southerners of the time who objected to the term "rebellion." But if I'm wrong about that, then just who was "Johnny Reb," and what was a "rebel yell"? ;-)
What acts of force before secession? The only acts of force before secession that I'm aware of were Anderson's troops charging laborers in Fort Sumter with bayonets and fighting with and overcoming the schooner captain, which is basically piracy. After the passage of secession by state conventions but before the the people of the states involved voted on it, some states did take action to protect themselves by taking possession of forts and arsenals, such as in Texas and Virginia and maybe other places. For example, a show of overwhelming force was used in Texas to force the federal troops there to leave the state after the secession convention voted for secession.
After secession, those properties and troops would no more automatically belong to Southern states than would, for example property owned by a citizen of France.
Seceded states were no longer bound by the Constitution than we were to Great Britain after the Revolutionary War or Texas was subject to the rule of the Mexican Constitution after San Jacinto. As such, the states had ultimate control of who owned what within their boundaries. Look at all the nationalizations of US owned property that have occurred in countries all around the globe, while the US did little or nothing about it.
... no federal reinforcements were sent by President Buchanan
Ignoring the Star of the West, are we?
By the way, to my knowledge there were no Southerners of the time who objected to the term "rebellion."
I imagine there were a great number of people both North and South who thought that the secession of a state was constitutional and not a rebellion. As Union general and later president, Rutherford Hayes said "The truth is, the men of the South believed in their theory of the Constitution. There was plausibility, perhaps more than plausibility, in the States' rights doctrine under the terms and in the history of the Constitution." Let's look at some of that history. From the New York ratification document [Link]:
Ratification of the Constitution by the State of New York; July 26, 1788.
WE the Delegates of the People of the State of New York, duly elected and Met in Convention, having maturely considered the Constitution for the United States of America, agreed to on the seventeenth day of September, in the year One thousand Seven hundred and Eighty seven, by the Convention then assembled at Philadelphia in the Common-wealth of Pennsylvania (a Copy whereof precedes these presents) and having also seriously and deliberately considered the present situation of the United States, Do declare and make known. ...
That the Powers of Government may be reassumed by the People, whensoever it shall become necessary to their Happiness; ...
... Under these impressions and declaring that the rights aforesaid cannot be abridged or violated, and that the Explanations aforesaid are consistent with the said Constitution ... We the said Delegates, in the Name and in the behalf of the People of the State of New York Do by these presents Assent to and Ratify the said Constitution.
Looks like Hayes was right.