IF WE USE THE LIST EDITOR TO PERSONALIZE OUR DROP-DOWN MENU OF OTHER STAFF ACTIVITIES, WILL WE BE ABLE TO CHANGE THE LIST LATER?

You may edit existing entries, but it becomes increasingly difficult to do as time passes. Before doing so, you must consider previous records tied to that entry before editing. Editing to correct spelling of an entry is fine, but you never want to edit one activity to reflect a different activity, because that would change all the existing records tied to former activity. In addition, you will not be able to delete any activity that has a record tied to it, unless you find those records and edit or delete them before doing so. This is to protect any data that may have been entered under the old activity you assigned to the drop down list.