Change up? Really?
I think he needs more debate prep.
A few days before the debate, he told us he's was probably going to make nice at this debate...and for the most part, he did.
He complimented Carly's looks, he was nice to Jeb, very nice to Carson, nice to Hugh Hewitt.
The reason for his being "nice" is because he knew everyone was going to attack, so he, by being nice, created a situation in which his opponents risked appearing as bullies.
In transactional terms, when he flattered Carly and she still looked bitter and dour, the impression was not lost on the audience (even if it was only noticed subconsciously).
It made him appear likable and made her appear angry.