The simple answer is no, you cannot. While in some cases it seems that being able to edit an active LifePak would be a useful feature, being able to do so would cause a host of problems for Mobile Users and LifePak Creators alike.
However, if you notice something you would like to change, remove, or otherwise edit, there is a way to fix it. Simply copy the LifePak and make the desired changes to the copy, then publish. This will create a new LifePak available for download. It will not replace the other LifePak, however, meaning that in most cases, Mobile Users will need to be notified that there is an updated version of a LifePak.