Not sure if this will answer your question but hopefully it will point some of us in the right direction. Many thanks to superstar Splunker Cindy McCririe!
My situation was similar but not identical which is why I'm not sure I will answer the original question.
renaming would fail with the same empty column, as would
fieldformat "Expected Value" = "$" + tostring("Expected Value","Commas")
but THIS works. . .
| eval "Expected Value" = round(Number * (Probability/100))
| fieldformat "Expected Value" = "$" + tostring('Expected Value',"Commas")
(Note the single quotes instead of double quotes in the fieldformat command)
| table Number, Probability, "Expected Value"
Hope that helps!
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