The legal division is between law enforcement officers (or some similar expression, defined by law), and everybody else. A security guard falls in the category "everybody else", so like everybody else, they can use force to defend themselves from an attempted murder. Nevada law simply defines "security guard" as "a person employed as a watchman, guard, security consultant, patrol officer or in any other similar position". The main reason for mentioning them at all is to exclude them from license-related laws applicable to private investigators and security consultants. This section of Nevada law defines those who have "powers of peace officers" – it doesn't include security guards or private investigators. One important distinction, stated here, is that
If necessary to prevent escape, an officer may, after giving a
warning, if feasible, use deadly force to effect the arrest of a
person only if there is probable cause to believe that the person:
1. Has committed a felony which involves the infliction or threat of serious bodily harm or the use of deadly force; or 2. Poses a threat
of serious bodily harm to the officer or to others.
An ordinary person cannot do this, instead that can use deadly force in self-defense, and not to effect an arrest.
The law does not allow anybody, including officers, to do otherwise-prohibited things unreasonably. The law does allow everybody to discriminate, except in specific cases such as you cannot discriminate based on race when hiring or beating a person (in the later case, it's called a "hate crime"). Questions about trespassing generally arise in connection with a rowdy person in a public place such as a bar, which are deemed to be "public accommodations". You are not allowed to discriminate on the basis of race in access to public accommodations, therefore you cannot eject a person for being the wrong race. However, your home is not a public accommodation, so you are not required to be racially-neutral w.r.t. your home. There is no LEO exception with respect to non-discrimination requirements.; there is no ordinary-person exception either. As for trespass warnings, the law says
A sufficient warning against trespassing, within the meaning of this
section, is given by any of the following methods:...By the owner or
occupant of the land or building making an oral or written demand to
any guest to vacate the land or building.