If you want to replace the salutation Bas uses with alternatives, you can do so as follows.
Remove the salutation and surname variable from every template where you want the changes applied. In the example below, that's the field with "heer" and "de Jong".
Replace this with the following code:
{% if customer.primaryContactPerson.salutation == 'heer' %} Mr (variable surname)
{% elseif customer.primaryContactPerson.salutation == 'mevrouw' %}
Dear Mrs (variable surname)
{% else %}
(variable salutation) (variable surname)
{% endif %}
You can extend this list if you like by duplicating the lines with {%elseif. You replace the 'heer' part with any other salutation Bas has, and this will be replaced with whatever you enter in the place where we've given Mr as an example here. After entering this in the editor, the example above looks as follows.
You'll find the data in the code (variable surname) and (variable salutation) here in the editor.
If you only want to replace one salutation, remove the line with the {% elseif.