Hi Hind

I don't believe it is possible to edit the workflow actions box, as this is added to the form at runtime. You can create your own task actions box and use it instead of the automatically generated one.

To allow a user to save instead of submit, I suggest you create 2 buttons (Save & Submit). You can then configure different rules for each (i.e. you don't need to validate on Save).

The question then becomes what happens after a user saves. Do you let them close the form and come back to later to complete? If so you will need to think about a mechanism to allow then to find and re-open the form. You could send them an email with a link, or give them access to another form that lists all of their un-submitted forms. You also need to think about how you would load any existing saved data when they re-open the form (e.g. you will probably need to use a form parameter to access the ID, and maybe another form state to have a different form initialize rule)