Yes you can. You can add, edit and delete assignments and tasks, resources etc. during a program.
But remember to be careful if you are about to delete anything. Maybe some learners already done a task that you want to delete? What would you do with the input from the learner? And how do you tell the learner that he/she needs to re-do the task again?
And if you want to add something - keep it locked until you are completely done. Then unlock it and make an announcement about it to inform your learners.