Hi,
Unfortunately, Reporting Services doesn't provide with any feature for doing such a formatting.
Basically, Reporting Services displays data within text boxes. There is no support for using multiple style format within a text box.
The only solution would be to build a rdl file on the fly and define as many textboxes as necessary when the data style format changes. No need to say that it is quite complicate and unefficient.

Hopefully, a future version of Reporting Services will be able to handle html formatting within a text box.

Regards,

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Frederic LATOUR
ENESYS