You should be fine taking CLEP and DSST tests prior to applying to one of the "Big Three" schools. I took a few CLEPs before applying and got the credit without any problem. I went ahead and specified TESC as my institution when I took the CLEPs even though I had not applied at that time. The only concern is that if you haven't applied and they don't know who you are they might file away your scores and not pick them up when you apply. Application only costs $75.00, so you should be able to do that pretty much any time. Worst case, you can pay CLEP $20.00 to send a transcript.