I think the best way to accomplish what you want is to use ASP.NET Themes. You can create a skin file with a RadRotator declaration inside it with the item template and all other settings except the DataSourceID property. A data source cannot be set from a skin, so you will need to set it manually on all pages that use this rotator theme. However, you should be able to set everything else (rotator type, size, template) from the theme.
If you do not wish to set the data source of all "child" rotators, then the only solution is to create a new control, which inherits from RadRotator, set datasource an all other settings in the code of the new control, and then use it instead of the normal RadRotator on your pages.
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