When you modify symbol styles in a projects, these styles will by available only in that project. However, you can make your own default symbol styles and use them for the new projects. In order to do that, you will be needing to modify the template.
To modify the template
From the <MagicDraw installation directory>\templates, open the template.mdzip.
In the Project Options dialog, modify symbol styles.
Save the template.
You can create and define your own project and use it as template.
After you define your desired symbol styles, you can use them in your new projects. All you need to do is to create project from template.
To create a project from template
Do one of the following:
From the File menu, select New Project.
On the main toolbar, click the New Project button.
Press Ctrl + Shift + N.
Select the Project from Template in the Other domain.