If you're going to change you intend on naming just your Minecraft username to CrashCourse and making videos with that username, that's perfectly fine.
If you plan on making videos with CrashCourse as your YouTube handle you'll likely run into problems if your channel begins to grow (which is likely what you want anyways) because of the Crash Course show by John and Hank Green. They're licensed under PBS Digital Studios so they more than likely have rights to that name.
Just be original! If your content is good people will watch it because of the videos that you make, not the name that you choose.
