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Tip: You might setup a special transition screen to mainly copy those fields to the newly created issue. So it feels more like it would be the create screen of the new issue. In that case, you won't show those fields on the origin issue, but reset them again afterwards (just empty or back to the default value), see Copy within the Origin Issue.
For 'Copy from the Origin Issue to the New Issue' append & prepend do only make sense, if the target field contains already a default value. So in practice append or prepend are more often used for 'Copy within the Origin Issue'. If at all.
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