I believe you can make substitutions up through the first team leaders meeting at the event. Someone can correct me if I'm wrong.
I tried to check the current entries to find the list of available substitutes and the link is broken
I can go to the event page and click on other links but the entries link is broken/bad domain?
http://www.isu.org/en/single-and-pa...su-junior-grand-prix-of-figure-skating-zagreb
Invalid Domain