There are three events for every object type. add:type, change:type, and destroy:type. Registering a function for the change:rollabletable event will work, but it will only fire when you change the table's name, or change the visibility to players. change:tableitem will fire when you change the image, name, or weight of an item in the table. add:tableitem will fire when you add a table item to the rollable table, and destroy:tableitem will fire when you remove a table item from the rollable table. If you want an event to react to rolling on the rollable table, you'll need to inspect chat:message events to find it. Changing the displayed side of a rollable token should fire change:graphic.