Is there anyway to change the standard SQL SERVER reports? And/OR See the SQL Behind it? SQL SERVER (through Management Studio) offers quite a few standard reports, but I don't see how you could change the reports. I don't even see an option for extracting/obtaining the SQL Code behind it. 

Is there any way to achieve this? Specifically, I am more interested in security reports (although it'd be nice to get code for all of them). 

Thank you in advance
Yes, run a Profiler trace while you run the report. It's just plain old T-SQL.

(Source: that's how I wrote the Performance Dashboard Reports chapter in the book SQL Server 2008 Internals and Troubleshooting.)