Edward.
no
Jacob and Bella's friendship didn't change after she found out he was a warewolf.
Bella had Renesme right before she was was changed. Giving birth to Renesme basically killed Bella so Edward had to change her in order to save her.
SPOLIER ALERT!Edward is the one who changes Bella!
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There is no exact year but it's the year after Bella graduates.
Bella was going to die when she gave birth to Renesmee. So he changed her to save her.
He sucked her blood.
gives him permission to change Bella because she was on verge of dying
I wouldn't change anything about Bella because the way she is, is why Edward loves her so much. But I would change some things about Kristen Stewart - her acting is really not that great.
to change her
no, this is not possible.