Yes this is possible.

You can add the total value of multiple items as one item to the monthly data layout.

Creating monthly data custom fields

1. Export / Import > Click "Create Output Layout" next to "Monthly Data [CSV]">  Monthly Data Custom Item> [+ New] and register the following contents.

Custom item name
Enter the name of the item.

Calculation unit

• Hours ... Select when creating items related to "working hours".
• Day …… Select when creating an item related to “Number of days”.
• Numerical values ​​... Items related to numerical values ​​other than the above are here. (Ex. Estimated transportation costs, number of counts, etc.)

Calculation result
Please check as appropriate according to your wishes.

Fixed value
Enter if you want to use a fixed value.

2. Next, in "Please select the item to add." , Check the "+" column of the item you want to add and register it.

Creating / importing monthly data layout

Click "Monthly Data Layout Settings" at the top left of the screen, and click [+ New] or a row of an existing layout> From the [Edit] screen, the item you created earlier has been added as a choice, so select it and click [ I will register. 

Export / Import > From "Monthly Data [CSV]", specify the layout including the created items and export the data.