title: Overwriting Python Path in xlwings
body: <p>I have two repositories in my file structure R1 and R2.  Repository 1 (R1) is in my PYTHONPATH.</p>
  
  <p>I'm trying out xlwings which works wonderfully when I run from Python to change an Excel file.  However, I'm having issues with running scripts from Repository 2 (R2).</p>
  
  <p>When I put the path to R2 in PYTHONPATH in the xlwings addin it seems to be <em>appending</em> R2 onto the original PYTHONPATH and since R1 is first it seems to be defaulting to R1 when importing.</p>
  
  <p>Is there a way to (locally) overwrite the PYTHONPATH just for that xlwings instance well keeping R1 in my system PYTHONPATH?</p>