Hi,
We can create a custom ASP.NET page e.g. ApplPage1.aspx and then let user navigate to this page like this,
<UrlAction Url="_layouts/TestProject/ApplPage1.aspx">
Now in your Page.Load event of ApplPage1.aspx, we can use If/else or switch statement to navigate user to website you want to navigate him.
Here is a similar thread for your reference:
http://sharepoint.stackexchange.com/questions/55426/custom-action-with-dynamic-urlaction
More information:
http://weblogs.asp.net/jan/using-the-current-page-url-in-the-urlaction-of-a-sharepoint-feature
Best regards
Dennis Guo
TechNet Community Support
