Here is my take:
- Rerolling an affix will make the item Account Bound -> pretty certain
- You can choose which affix to replace -> that was said in one of the presentations or interviews
- You can choose with what affix to replace the selected affix -> probably not
- You can reroll more than one affix on an item -> probably not, pretty sure Josh said: 'you can reroll ONE affix'; but may be he meant 'at a time'?
- You can reroll the same affix slot more than once -> not sure, don't think that was ever mentioned
- The possible affix value range is based on the items ilvl -> probable as it makes sense IMO