Override field to a text span inside a button

Would like to add an override field to a text span inside a button. Is it possible? I use an icon font, so a background image inside the button is not an alternative. The text field within the button settings is overriding the whole text and removes the text span.

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Screenshot 2020-09-08 at 08.59.03

Screenshot 2020-09-08 at 08.59.22