You can add your own fortunes to the stack, but you will have to unlock the fortune field and the category field if you want to write into them. If you have several new fortunes to enter, unlock these two fields at the beginning of the session, and donΓÇÖt forget to lock them again when you are finished.
As mentioned before, make sure that you keep categories together, in case you want to export your fortunes at some time in the future. ItΓÇÖs OK to create new categories.