hi. i also changed from performance, but i changed ages ago so i didnt keep my log book. but if your changing now, you definately should, and show the reasons why your changing. you should include research from the play, examples of other promos for the play, any symbolism, metaphors and themes and motifs etc. this will also help you with designing it. if you ever have any ideas, jot them down and include sketches of possible images etc. id also read the play and jot down what you think are the major scenes etc.
include mindmaps too, ppl love them. make sure you put in every thought you have, no matter how irrelevant it may seem, because unlike performance, the examiners will be looking through your logbook thoughaly, so you REALLY need to show your thinking process and how you got to your final piece.
im doing costume and ive even included skeches of possible layouts for my renderings.
maybe you could also take a look at reviews and good quotes about the play that you could use in you promo. im sure it would be good if you used real quotes instead of making them up.
hope i helped!