From the manual - are one of these what you are looking for?
"beforelayoutstart"
"afterlayoutstart"
Fired when the layout starts. "beforelayoutstart" fires just before On start of layout, and "afterlayoutstart" first just after. In both events, all instances on the layout are created and available to modify.
"beforeprojectstart"
"afterprojectstart"
Fired once only when the first layout in the project starts. "beforeprojectstart" fires before "beforelayoutstart" on the first layout, which in turn is before On start of layout triggers. "afterprojectstart" fires after "afterlayoutstart" on the first layout, which in turn is after On start of layout triggers. In both events, all instances on the first layout are created and available to modify.