PrimeFaces: how to make the theme dynamic

PrimeFaces: how to make the theme dynamic

I need to make the theme dynamic by the different users, currently, I find
the guide in http://www.developer.am/primefaces/?page=Applying%20a%20Theme
It says: In case you'd like to make the theme dynamic, define an EL
expression as the param value.
<context-param>
<param-name>primefaces.THEME</param-name>
<param-value>#{loggedInUser.preferences.theme}</param-value>
</context-param>
In my understanding, the theme will be changed by the different users,
right? Even I change the theme in preferences for the user, I have no need
to restart the middleware, the theme will be changed at once, right?
Please guide me, thanks in advance.