If I understand you correctly, you want to use only the comma as a separator for the tag cloud items. I am afraid that disabling the space as separator for the specified text is not supported by the RadTagCloud.
If you want to insert words with spaces in the tag cloud, you can manipulate its items collection either on the server-side or on the client-side instead of retrieving the words from a provided text.
The following sample shows how to add your items from the code-behind:
This online demo
shows how to add items in the tag cloud via the client-side API of the control.
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