Question

When you drag a web user control onto your design surface, it will automatically assigns the tagprefix = uc1.

Does anyone know how to change the default tagprefix for all web user controls
you drag onto a web form?

Answer 1

Adding User Controls to a Web Forms Page

You have to Register the control below the Page directive like below.

<%@ Register TagPrefix="Guest" TagName="GuestExample" Src="~/YourControl.ascx" %>

and then change the TagPrefix and TagName as per your requirement.

Example

<Guest:GuestExample ID="ID" runat="server" />

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Instead of duplicating them on all your pages, just declare them once
within the new pages->controls section with the web.config file of
your application:

<?xml version="1.0"?>
<configuration>
  <system.web>
    <pages>
      <controls>
        <add tagPrefix="Guest" src="~/YourControl.ascx" tagName="GuestExample"/>
      </controls>
    </pages>
  </system.web>
</configuration>