Can one dismiss their Psionic Focus voluntarily?

I’d like your opinions on this as I’m disagreeing with a ruling made by my GM.

The full question is: Can a character voluntarily dismiss their psionic focus and, if so, what type of action would it be?

The rules clearly state how to gain or expend your focus. They also explain in which situations you would lose it involuntarily, for example if you become unconscious. But not a word about whether you can actually dismiss your focus.

Why would you want to dismiss your focus? For example, at the beginning of an encounter when you know for sure that one/some/all of your opponents either resist, are immune to or (even better!) are vulnerable to a specific energy type.

As you know, when a psionic character gains his focus, he must choose an energy type. The exception being the Kineticist. So if a player wants his character to dismiss his focus in order to subsequently gain it with a different energy type, what happens?

My GM says, no problem, you can do that. You just need to concentrate a bit, so it would be a move action.

I’m thinking, if someone can physically drop an item as a free action, why couldn’t they also drop something psionically as a free action?

I’m also thinking: if a barbarian can end a rage (in which some of her body may have physically changed into bestial forms) as a free action, then why can’t psionic characters just drop something which is purely mental also as a free action?

And now to make matters even worse: what happens if you have Psicrystal Containment or Deep Focus? How long does it take to drop two focii? If you’re focused twice, with either of these methods, can you gain two energy types? I would say no on this one.

Food for thought. Thanks for your input. C.