Simplenews does not apply templates and does not resend
About You Second Issue - Here is a "dirty" solution.


Go to phpMyAdmin and find simplenews_newsletters table
Edit that table and change s_status on the newsletter you want from 2 to 0.



s_status - 2 Newsletter has been sent

s_status - 0 Newsletter has not been sent

s_status - 1 Sending Newsletter