You're welcome! To answer your questions in order:
Yes, you can reroll more than once; that particular option doesn't interact with marked attributes.
Generally speaking, he character creation is designed to be all "in order", so if you settle on a result and decide not to spend, you can't take backsies. That being said, if your table is fine with you going backward and undoing that roll, it's likely not going to break anything, but I wanted to avoid having to track previous rolls or increasing choice anxiety in undoing past decisions.