Can you please post links to where you read that day traders can carry back NOLs 2 or 5 years?

Where have you looked at IRS.gov?  Have you tried Pub 536?

Regarding the specific section that deals with mark to market elections would IRC 475.  The specific section that deals with NOLs would be IRC 172.

For your second question, its unclear what prior year NOLs you would be referring to.

However, a trader making a mark to market election under IRC 475(f) is also required to file Form 3115, for a change in accounting method.  The change code is DCN 64.  As you work through Form 3115 and the 481(a) adjustment I think it might answer some of your questions regarding how to treat a negative income adjustment.