In short, to answer your questions:
1. No
2. Yes - until April 6 (Beginning April 7, a $25 fee will be charged for changes made on nwa.com for less than 30 days prior to departure). Platinum elites are waived from any change fees.

Unfortunately changing reservation on nwa.com is only limited to NW flights only for now. It is very likely you'll have to scoop out $200 ($50/ticket) to change to the later flight. Most award tickets flown on partner airlines cannot be changed online.