Please let me know if it is possible to set a global skin for all RadControls in my web application instead of setting the skin property to individual RadControls?
Yes, it is possible to set a global skin which is applicable to all the RadControls under your project. To set a global skin, you need to configure the web settings at the time of creating your new website as follows.
When you create a New Website with "RadControls web Site" template, you will get a Project Configuration Wizard as shown in the attachment. Under its Web Settings, you can choose a default skin for your entire web site.