title: Edit existing named region with openxlsx
body: <p>I have an existing workbook with some data and charts.
  I'm using <code>openxlsx</code> to add recent data and would like to edit an existing named range to reflect this (the charts use this named region).</p>
  
  <p>I tried using <code>writeData</code> and <code>createNamedRegion</code> to do that, but I receive the error message "Error in (...): Named region with name 'named_region' already exists!"</p>
  
  <pre><code>library(openxlsx)
  filename &lt;- 'test.xlsx'
  wb &lt;- createWorkbook()
  addWorksheet(wb, sheetName = 'test')
  writeData(wb, sheet='test', x=data.frame(a=1:3,b=2:4), startCol=1, startRow=1,
            colNames=T, rowNames=F, name='named_region')
  saveWorkbook(wb, file=filename, overwrite=TRUE)
  
  wb &lt;- loadWorkbook(file = filename)
  writeData(wb, sheet='test', x = data.frame(a=4:5,b=5:6),
            startRow=5, colNames=F, rowNames=FALSE, keepNA=FALSE) # ok
  
  # not ok
  # writeData(wb, sheet='test', x = data.frame(a=4:5,b=5:6),
  #           startRow=5, colNames=F, rowNames=FALSE, keepNA=FALSE, name='named_region') 
  # createNamedRegion(wb, sheet='test', cols=1, rows=2:6, name='named_region')
  
  saveWorkbook(wb, file=filename, overwrite=TRUE)
  </code></pre>