I rewrite BlockTree:

                BlockTree original = (BlockTree) node;
                List<StatementTree> list = new ArrayList<StatementTree>();
                list.add(original.getStatements().get(0));
                list.add(original.getStatements().get(0));
                modified = make.Block(list, false);
                rewrite(node, modified);

That is, the new list contains two references to a single statement in the original list.
The input is:

    int x;

    void m1() {
        x++;
    }

The log is:

original: {
    x++;
}
modified: {
    x++;
    x++;
}

However, the source is not changed.