title: Modify a single cell value in dplyr
body: <p>Let's say I have the following dataset:</p>
  
  <pre><code>dat &lt;- read.table(text="id_1 id_2 
                    123 NA
                    456 NA
                    NA 3
                    NA 1
                    NA 1", header=T)
  </code></pre>
  
  <p>I'd like to change the <code>id_1</code> value for the first row.  I'd like to do something like this: </p>
  
  <pre><code>dat %&gt;% slice(1) %&gt;% mutate(id_1 == "new_id") %&gt;% unslice()
  </code></pre>
  
  <p>However there doesn't appear to be an <code>unslice</code> command, so I'm left with a dataframe that has a single row (the modified).  Is there a clean way do get back the original dataset after modification in-place?</p>