Can students update assignments over time and can I change the assignment over time?

[pbellar]

This is a three part question.

1. Can I start an assignment (online submission assignment) for the purposes of participation over the month and be able to add to the assignment (additional questions, etc)?

2. Can a student save their progress of an assignment over time for this assignment? 

3. If I do add additional questions to this assignment over time (w/o changing any prior questions), will it change their  answers to prior questions?

Thanks for any clarification.