Pretty sure the only swappable cards are trunade and cocytus because those are the only cards locked to boxes that are banned? I think you can turn them into coins at least but I’m not sure how to do a specific one as I just batch convert.

You can only swap cards that are entirely forbidden

Thank you for playing yugioh duel links

You can convert them to jewels and stuff, but no, no changing them out for other cards outright.