Do I need to do special tricks to use https?

Is there a simple way the transition between the parties with http to https?

You mainly need to care about the URL generation using Yii functions.

By default, Yii generates relative URLs. You can call Yii::app()->createAbsoluteUrl() to generate an absolute URL with the specified schema.

You can use Yii::app()->request->isSecureConnection to determine if connection secure or not and redirect with Yii::app()->request->redirect if current state is not what you want.

If you are using nginx you need to pass fastcgi_param HTTPS on; for your secure places.