@Override
	public boolean setOpIndex(int opIndex) {

		if (editRef != null) {
			throw new IllegalStateException("setOpIndex only permitted for ADD case");
		}

		isValidState = false;
		this.opIndex = opIndex;

		if (opIndex == EditReferencesProvider.MNEMONIC_OPINDEX) {
			return false;
		}

		isValidState = true;
		return true;
	}
Pop up the data tree dialog so the user can choose the external program.
Ghidra/Features/Base/src/main/java/ghidra/app/plugin/core/references/EditExternalReferencePanel.java