Strictly speaking, I believe the reactance (part of impedance)
equations apply to any variation in current magnitude. Their appropriate
application does not in any way require reversing the charge.

1) I think one needs to define the term "alternating current" by its
phenomena rather than define it by what applies to "AC". In other words,
define AC as alternating current -rather than defining AC as "anything
requiring an impedance calculation because of its magnitude variation".
( OK, all scientific definitions require definitions in terms of other
defined concepts; thus voltage and charge are defined in terms of force.
And yes, any phenomena in its purest defined form uses the fewest of the
core units, and only the core units, of the measuring system. And yes,
since, unlike in the British ft-sec-lb system, force is not a core unit of
the metric kg-sec-m system, one cannot be as "pure" in the metric system
with many definitions as one can be in the British system, "decile"
convenience notwithstanding)

2) There are two phenomena and two descriptive words if one uses the
mathematical description of the changes associated with current: changes in
current__ _direction_ __and changes in current__ _magnitude_.__

There are three (or more) phenomena if one uses only the two descriptive
terms__ _AC_ __and__ _DC_,__ well evidenced in this thread: changes in direction and
magnitude, changes in magnitude only, or no changes in either magnitude or
direction. Three phenomena defined using only two words for those three
cannot be specific and exclusive enough for a rigorous definition. The
middle condition, the overlap as it were, ends up wanting.

3) In the definition approach to a phenomena, one deals with the
descriptive term and the phenomena itself and ignores the present attached
effects. Once the definition is had, then the phenomena's interaction with
other phenomena can be determined. Yes, having such rigor in a definition
can be more complicated in its application.

In the application approach to defining a phenomena, one defines by
addressing what equations, etc., apply to the condition. In this approach,
you end up in circular arguments, chasing your tail. Something always will
not fit. Like changes in magnitude without changes in direction.