Can Custom Themes Be Designed or Imported via API for Gamma Integration?

Can a theme be designed via api? Use case is gamma api is integrated in my platform. All generations currently come from pur gamma acct. Some users have their own gamma acct and we are allowing them to plug in their api key, but our prompt instructions reference custom themes we've built for them to use which they obviously don't have in their gamma account....didn't know if we could send those theme instructions via api or have them import the theme another way - as like a step two when adding their api key