要通過ItemDecoration改變列表項的顯示效果，可以創建一個自定義的ItemDecoration類，并重寫其onDraw()和onDrawOver()方法來實現想要的效果。例如，可以在onDraw()方法中繪制分隔線或背景色，或者在onDrawOver()方法中繪制懸浮的標簽等。然后將該ItemDecoration類應用到RecyclerView中即可。

以下是一個示例代碼，演示如何創建一個自定義的ItemDecoration類來繪制分隔線：

public class DividerItemDecoration extends RecyclerView.ItemDecoration {
    private Drawable divider;

    public DividerItemDecoration(Context context) {
        divider = ContextCompat.getDrawable(context, R.drawable.divider);
    }

    @Override
    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
        int left = parent.getPaddingLeft();
        int right = parent.getWidth() - parent.getPaddingRight();

        for (int i = 0; i < parent.getChildCount(); i++) {
            View child = parent.getChildAt(i);
            RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams();
            int top = child.getBottom() + params.bottomMargin;
            int bottom = top + divider.getIntrinsicHeight();
            divider.setBounds(left, top, right, bottom);
            divider.draw(c);
        }
    }
}

然后在RecyclerView中應用該ItemDecoration類：

RecyclerView recyclerView = findViewById(R.id.recycler_view);
recyclerView.addItemDecoration(new DividerItemDecoration(this));

這樣就可以在RecyclerView中顯示分隔線了。您可以根據自己的需求和創意，定制不同的ItemDecoration類來改變列表項的顯示效果。