Volley Fire in Piquet/Band of Brothers II

I have been going through BoBII rules in detail as part of the "specialization" program. According to BoBII some bow armed units may opt to fire overhead. This is called 'Volley Fire' and can be undertaken by any unit designated with 'VF' capability in the army listing. Volley fire dramatically increases the long range band from 6-12" to 6-24" but reduces the fire modifiers.

I was not sure if a unit could switch between volley fire and "normal" direct fire during the course of a game. For instance, consider this example:

An unit of English Retinue Longbowmen (Hundred Years' War) in Chevron formation declare and conduct VF at (extended) long range when a missile reload card appears. The unit then reloads using this card. When the next card appears in the same turn, they opt to conduct direct fire instead.

Is this scenario valid under the rules?

Here is Peter's answer:

Certainly. The operative term is "may", not "must". Volley fire is high angle fire used to increase the range of he archery at the cost of a decrease in penetrating power.