Not from within SketchUp.
The number separator is determined by internationalization settings at the operating system level. On Windows 10, find this through:
<Start Menu> --> Settings --> “Additional date, time, & regional settings”
This will bring up the “Control Panel > Clock and Region” window. Now click on
“Change Date, time, or number formats” bringing up the “Region” window. Click on “Additional Settings” and you should see something like:
I’ve highlighted the setting you need to change in yellow. To change it, just enter the character you want as your list separator, then click the OK button.
Note that this might have unintended consequences - especially in other programs! The * character is often used for multiplication. Don’t be surprised if, after making this change, other programs that allow you to embed in-line computation in text fields fail when you try to use multiplication!
If SketchUp is active when you make your changes, you’ll likely need to quit and restart before the change is recognized by SketchUp.