If your are going to replace all of the connection strings with news ones for production environment, you can simply replace all connection strings with production ones using this syntax:
<configuration xmlns:xdt="http://schemas.microsoft.com/XML-Document-Transform">
<connectionStrings xdt:Transform="Replace">
<!-- production environment config --->
<add name="ApplicationServices" connectionString="data source=.\SQLEXPRESS;Integrated Security=SSPI;AttachDBFilename=|DataDirectory|\aspnetdb.mdf;User Instance=true"
providerName="System.Data.SqlClient" />
<add name="Testing1" connectionString="Data Source=test;Initial Catalog=TestDatabase;Integrated Security=True"
providerName="System.Data.SqlClient" />
</connectionStrings>
....
Information for this answer are brought from this answer and this blog post.
notice: As others explained already, this setting will apply only when application publishes not when running/debugging it (by hitting F5).