The ConvertInlineStylesToAttributes is a complex filter and it is not so easy to be implemented in an earlier builds.
As being an owner of Developer License with subscription you can download the source code of Telerik.Web.UI.dll and implement your own custom content filter
using as a base the code of the ConvertInlineStylesToAttributes filter. This filter is located in the \Editor\RadEditor\EditorFiltersManager.js. It also use the convertAttribute, convertBorderAttribute, convertCSSProperty and convertTypeAttribute functions the declarations of which are available in the \Editor\RadEditor\0EditorUtils.js file.
the Telerik team
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