Hi Eric, thanks for the question.
They are not customizable, no. If that is something you'd like to see in a future release, feel free to create an
Idea in Aha and our team will take it under consideration for future enhancements.
In the meantime, I thought I would mention that the tab names are text fields that support unicode characters. If there is any
unicode emoji (click here for a full list) that would be comparable to the custom icon(s) you wish to use, then you could copy & paste them into your tab name (see attached for an example). Check the matrix on the Unicode Consortium site I linked to ensure the browser you're using will render the emoji before using them.
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Brennan Fox
Product Quality @ IBM Cognos Analytics with Watson
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