I don't want to change the structure of the wiki too much, so I prefer to edit the actions tiddler instead of the button tiddler.
And thank you for making the example wiki with the button.
However, in the meantime I thought of another way of solving it. instead of adding some fields to the journal tiddlers from the start, I have put checkboxes in the text field, that add the exercised field with a "yes" value when checked (and other desired fields to track).
I am going to use this for counting how many days I exercise and do other habits. In addition, I have hidden these checkboxes with another checkbox that makes the field "log" when checked. This way I can count days where, log has "yes" and exercise is not "yes" (including non existing). This way I only count these fields for days I do log (no ambitions on weekends).
<$checkbox field="log" checked="yes" unchecked="no" default="no"> Log</$checkbox>
<$reveal type="match" state="!!log" text="yes">
* <$checkbox field="exercise" checked="yes" unchecked="no" default="no"> trænede </$checkbox>
* <$checkbox field="meditation" checked="yes" unchecked="no" default="no"> mediterede</$checkbox>
* <$checkbox field="reading" checked="yes" unchecked="no" default="no"> læsning</$checkbox>
* <$checkbox field="project-work" checked="yes" unchecked="no" default="no"> projekt fremgang </$checkbox>
* <$checkbox field="journal" checked="yes" unchecked="no" default="no"> dagbog</$checkbox>
</$reveal>
But thank you for your help.