I've heard that you should not take all the old strings off, then put the new strings on. The lack of string tension, and then putting the new strings on, will mess up the intonation/truss adjustment. I had always taken all the strings off first, then put the new ones on. I could clean the fret board while the strings were off. Now, since I heard that I change one string at a time, so all the tension doesn't all go away at once. What is correct?