https://plugins.jetbrains.com/docs/intellij/working-with-text.html#safely-replacing-selected-text-in-the-document seems pretty close

https://github.com/JetBrains/intellij-community/blob/4bec5270ac967904d8a874eb5d12749e8e3510a2/platform/platform-impl/src/com/intellij/openapi/editor/actions/CopyAction.java#L111

https://github.com/JetBrains/intellij-community/blob/0e2aa4030ee763c9b0c828f0b5119f4cdcc66f35/platform/editor-ui-api/src/com/intellij/openapi/ide/CopyPasteManager.java

public abstract void setContents(@NotNull Transferable content); Transferrable content = ...; CopyPasteManager.getInstance().setContents(content);

https://github.com/JetBrains/intellij-community/search?q=setContents

CopyPasteManager.getInstance().setContents(new StringSelection("hello world"));

So the real q is: how do i "cross the streams" and run some code in the cursive process?

Something like this? https://clojurians.slack.com/archives/C0744GXCJ/p1644978986077219

(let [s (java.util.UUID/randomUUID)]
  (.setContents (.getSystemClipboard (java.awt.Toolkit/getDefaultToolkit))
    (java.awt.datatransfer.StringSelection (str s))
    nil))

I’m planning to update the REPL commands to have options to do this more automatically, but that’s a nice workaround in the meantime.