SETVALUE allows you to fix the value of a variable. At the same time, it also allows you to change the values when the question appears without showing the already set value.
It seems you want to fix a value of a variable and show respondent the already set value, he can change the values if he wants to. Right?
In this case, you can set the value using java-script (document ready) and the script needs to be written on each specific page. The value will appear on the survey and the respondent can also change that.
Hope this is the information you were looking for.