You'll have to write some PHP code for this. The best way is to use an advanced theme which overrides the form(...) theme function, check $this->template and $this->context['part'], and then if appropriate modify the part of the $form variable responsible for that option, before calling through to the theme base class.
Welcome to the Q&A site for Question2Answer.
If you have a question about Q2A, please ask in English.
To report a bug, please create a new issue on Github or ask a question here with the bug tag.
If you just want to try Q2A, please use the demo site.