Yes, we can. SSRS allows developer to add custom code in your report. You can write the code directly into embedded VB.Net and call it using property expression or you can write a custom class library and refer it in report server. The advantage of first method is that it is simple and easy to use but disadvantage is that it is available for that report only. While the second method has advantage of being available for multiple reports but it has much of configuration overhead.

To write custom code, right click on Report Designer outside report body and select Properties and go to Code tab and you can write custom code here.

To add custom class library, right click on Report Designer outside report body and select Properties and go to Reference tab and add the reference by browsing to the assembly of your class library. Note that you need to create class library and then compile it before referencing it in your SSRS report.