i am not entire sure what you are asking about with the refresh case but the node types are always read dynamically:
https://github.com/jackalope/jackalope/blob/master/src/Jackalope/Node.php#L922

as for addMixin .. it uses addValue/setProperty to manipulate the property, so guess in the end it also ends up in _setValue:
https://github.com/jackalope/jackalope/blob/master/src/Jackalope/Node.php#L1010