Not sure if it has been stated elsewhere, but in the background section, for the Magical Experiment, there are no options to select the background’s special ability benifits.
Thanks.
Thanks for reporting this! We don’t support homebrew content yet, but I suspect we can support the example options in the short-term.
Full support for this background will come after homebrew support is available. 
Thanks
This background comes from Secrets of Magic, I didn’t think it was homebrewed.
It’s not homebrewed, but it includes the text, “You gain one special ability as a result of the magical experimentation. Work with the GM to select an appropriate ability from the following list or to come up with another special ability.”
Without homebrew support, we’ll only be able to support the listed options.
Thanks, now I understand the constraints of the builder.