In the subject you say "date and currency", in the post, you're only saying currency.
It's probably code out there (see bottom of reply) which will enable you to change regional settings, but I question why you think you need it.
If you're thinking about changing regional settings while the user is using your app, I think you should rethink your strategy. Consider that today, most people are having more than one application window open at the time, and changing regional settings will affect them all. This is usually not desirable.
To take it a bit further, where I live, some of my customers might need to change/switch regional settings during session to be able to import or interface with both legacy systems, and newer systems where the developers have been less internationally aware than desirable.
One will expect the system to run well on all locale.
But do be a bit more specific with what you want/need, then there's probably people that can answer.