They'll let you sign up for more than one applied course at a time. Hell, I'm currently enrolled in 3 applied courses right now (all of which start in Dec). At first I was pissed, then I called and complained that I was going to be deployed, blah blah blah. . POOF, enrollment for 3 of 4 right there, with the assumption that I"ll have the prereqs done prior to start.
The National Security one sucked.