The standard style of the comment box in Excel is a rectangular shape as shown below.
Now let us see how to customize the comment box shape using the Change Shape option in Excel 2016 & Excel 2013.
Add Change Shape to Office Ribbon
In order to change the shape of comment box, we need to add Change Shape option to Office Ribbon.
Step 1: Click File menu and select Options from the list.
Step 2: In the Excel Options screen, navigate to Customize Ribbon tab.
Step 3: Select All Commands for the “Choose commands from” dropdown list.
Step 4: In this example, we are going to add the Change Shape option under Insert menu. Let us create a new group under the Customize Ribbon and provide name as Change Comment Shape. Click the New Group button then use Rename button to enter a name.
Step 5: Now pick Change Shape from All Commands list and add this under Change Comment Shape group.
Now you should see the Change Shape command under Insert menu in Office Ribbon.
Change Shape of Comment box
Step 1: Insert a comment in Worksheet by using right click context menu or the option available as part of Review menu.
Step 2: Now select the comment box, navigate to Insert menu and click Change Shape.
Step 3: Pick a shape for the comment box from the shapes dropdown list.
The selected shape would replace the comment box as shown below.