My own advice would be to consider this tedium as a negative incentive to better manage your planning. If you’re overplanning so much that you’re (a) spending time filling out an agenda that you’ll never actually complete on time; then also (b) spending time moving every item on that agenda to the next day; and then (c) adding yet more tasks that potentially won’t be completed to that agenda, then it’s just not worth the bother.
Any task or project management system that makes it as easy as possible for you to put things off is just going to foster bad habits. Everyone needs to occasionally move things around or push back a deadline, but then everyone should also periodically be considering the pros and cons of their routines, too. Imagine if the Agenda developers were to agree to add your requested feature, but then went about it the same way you’ve described above…