There's an antisocial part of me that really loves stories like this. This would be a nightmare. Angst galore! "What did I do?" "This was 20 years ago, how am I supposed to remember?" "I can't let that happen again, but what will I change if I fix it?"
It'd be immediately worse for Lois but Clark would have issues too before long. With his memory he would have to fight the temptation to call or to send letters that could divert disasters.
