title: Changing ggplot2 legend title without altering graphical parameters
body: <p>I have found many topics about the legend title with ggplot2 but after a couple of hours I have not been able to handle my situation.</p>
  
  <p>Here is the dataset:</p>
  
  <pre><code>&gt; dat
    FACTOR1 FACTOR2 lsmean lower.CL upper.CL
  1       A      aa   26.2     25.6     26.8
  2       B      aa   24.8     23.9     25.7
  3       A      bb   26.0     25.2     26.7
  4       B      bb   24.9     23.9     25.9
  5       A      cc   24.4     23.9     24.8
  6       B      cc   23.9     22.9     25.0
  7       A      dd   24.9     24.3     25.6
  8       B      dd   23.2     22.3     24.0
  </code></pre>
  
  <p>And the graphic of interest:</p>
  
  <pre><code>gp0 &lt;- ggplot(dat, aes(x=FACTOR2, y=lsmean, group=FACTOR1, colour=FACTOR1)) 
  ( gp1 &lt;- gp0 +  geom_line(aes(linetype=FACTOR1), size=.6) + 
      geom_point(aes(shape=FACTOR1), size=3) + 
      geom_errorbar(aes(ymax=upper.CL, ymin=lower.CL), width=.1) +
      geom_errorbar(aes(ymax=upper.CL, ymin=lower.CL), width=.1) ) 
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/vvw3w.png" alt="gp1"></p>
  
  <p>If I use <code>scale_colour_manual()</code> to change the legend title then I get an unexpected additional legend:</p>
  
  <pre><code>gp1 + scale_colour_manual("NEW TITLE",values=c("red","blue"))
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/em05G.png" alt="gp1+"></p>
  
  <p>I suppress this additional legend with <code>scale_"aes"_manual("guide=none", values=...)</code> but I don't understand how to control the parameters (the style of points and lines):</p>
  
  <pre><code>gp1 + scale_colour_manual("NEW TITLE",values=c("red","blue")) +
      scale_shape_manual(guide = 'none', values=c(1,2))   + 
      scale_linetype_manual(guide = 'none', values=c(1,3))  
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/OZelr.png" alt="gp1++"></p>
  
  <p>Please how to reproduce the first plot with and only with a new legend title ?</p>