Remove the default Task Outcomes (Approved rejected)

• Create a new Task List Instance (new workflow wizard will help you do it)
• new Custom List Column with type OutcomeChoice

<Elements xmlns="http://schemas.microsoft.com/sharepoint/">  

  <Field

       ID="{a8229356-e367-4379-a6f7-f19fdca45cde}"

       Name="tatatatatata"

       DisplayName="tatatatata"

       Type="OutcomeChoice"

       Required="FALSE"

       Group="Custom Site Columns">

    <CHOICES>

      <CHOICE>very goodt</CHOICE>

      <CHOICE>good</CHOICE>

      <CHOICE>Average</CHOICE>    

      <CHOICE>Bad</CHOICE>

    </CHOICES>

  </Field>

</Elements>

• new ContentType Inherit from Workflow Task (SharePoint 2013)  (we will edit this later)
• Add the Custom Column to the contentType
• from the contentType Element.xml remove this string  003365C4474CAE8C42BCE396314E88E51F

So an ID like:
0x0108003365C4474CAE8C42BCE396314E88E51F00B237734C3B3E48D38A52DAAA52F56A8F  ==> 0x010800B237734C3B3E48D38A52DAAA52F56A

• Open the file Workflow.xaml with xml editor 
• find your <p:SingleTask
• change ContentTypeId to the new id you just modified (0x010800B237734C3B3E48D38A52DAAA52F56A)
• go to your TaskList instance and Add your contentType:

  <ContentTypeBinding ListUrl="Lists/InterventionList" RootWebOnly="FALSE" ContentTypeId="0x010800B237734C3B3E48D38A52DAAA52F56A" />

• Deploy your project and see the magic happens

Please leave a comment if you need clarifications