If you want simply to change the text on a menu you can something like that:
First, enclose the text into a text widget:
<screenSecondMenu onAction="cancel">
<text id="secondMenuText">%CANCEL%</text>
</screenSecondMenu>
Change the onAction called in onMessage():
this.screen.getSecondMenu().setOnAction("next");
Change the text displayed on second menu:
((Text) this.screen.getWidget("secondMenuText")).setText(Kuix.getMessage("NEXT"));