Updating the MaxRecordsForExportToExcel is a supported change; however, it is not supported to update it directly in the database.
You should be able to update it using the web services:
Organization organization = new Organization(); organization.Id = orgId; organization.MaxRecordsForExportToExcel = 300000; service.Update(organization);
You can also create a New report off of the advanced find you have saved. Run the Report and export the report to excel. This works in CRM 2011 online as well.
Thanks and regards