Thank you very much for updating your question. I think I understand the problem now.
Properties mapper has an upper limit of 20 distinct values that are displayed in the conversion details drop-down list. However, since you want to change the node style depending on label text, you can simple enter the desired text instead of choosing a value from the drop-down list. I.e. once you have added a new row using the green "+" button, click into the left column of the new row *close to its left border*. This will start direct editing instead of opening the drop-down list. However, even if the drop-down list is opened, it is still possible to directly enter text in the table cell instead of choosing a value from the drop-down list.
That said, using properties mapper in this way is rather inefficient. You should either
- add an additional data range for node properties to your spreadsheet where you map node IDs to custom properties like "Shape" and then define mappings for node styles based on that property, or
- select the nodes whose style you want to change in the editor area and then directly change their styles by right-clicking the desired style in the palette to open the style templates context menu and choosing "Apply" or "Apply Type".