Changing Sheet Names In Sql Server Reporting Services Excel Export
This is possible in SQL 2008 R2 and above – but if your company is not going to move to this any time soon, then this is not a viable option. R2 is a separate product, and is chargeable as an upgrade – it's not a service pack release.
However, there is an alternative that looks quite promising:
This solution is not for the faint hearted - but is a viable alternative to a costly upgrade. Essentially you customise the report design, adding to it an edited xml style sheet template (XSLT). When you then run the report, it outputs with the sheet names that you defined.