there isn't way how to change URL (switch to different page) in case of Alarm.
However you can use "hide_by" datapoint which is part of every HMI component. When the "hide_by" datapoint is ON the specified component won't be visible and vice versa:
It is beneficial to combine this feature with making your component out of standard Inkscape shapes - rectangles, circles, etc. (Extensions -> REXYGEN HMI -> Group Animaton (CTRL + J)).
Note: I recommend to use Layers in REXYGEN HMI Designer - just to keep the overlapping components "readable" and "editable" - https://wiki.inkscape.org/wiki/index.php/Layer_Dialog
There is also "0301-08 HMI Animation DEMO" example available which demonstrates all kinds of Group Animations.
Let me know if I can be of assistance.
PS: manual switching between multiple HMI pages is also possible - see another topic: https://forum.rexygen.com/topic/57/hmi-with-multiple-pages