Hi Kaori,
In Mendix you can't use the same show page activity to dynamically open pages based on a variable.
The decision would be the default to go for, even if that would lead to a lot of “show-page” activities.
You could also decide to navigate to the same page, but use conditional visibility or, for example, a list view with templates per specialization.
Or i suppose you could use a java action, although i generally would not recommend doing this because of the complexity and maintenance burden of java actions.
And there possibly are even more creative options, depending on the situation.
If you would like to know more, it would be helpful if you shared a little more on your specific situation.
I hope this helps.