Yes, you can do that using onBeforeEventRender event handler. Please take a look at the examples in the docs (the following link is for the Scheduler):
https://doc.daypilot.org/scheduler/event-customization/
Especially the "Accessing Event Data" section:
dp.events.list = [
{
start: "2016-03-15T00:00:00",
end: "2016-03-17T00:00:00",
id: "1",
text: "Event 1",
tags: { detail: "Detailed event description", type: "important" }
}
];
dp.onBeforeEventRender = function(args) {
args.data.cssClass = "test";
args.data.html = args.data.text + "<br/>" + args.data.tags.detail;
if (args.data.tags.type === "important") {
args.data.barColor = "red";
}
};
Let me know if this isn't what you are looking for.