Hi there,
Thanks for your query. If you are interested to add a new currency to the SP Property Extension then no default way to add it, but there is a workaround you can try.
Here is how to change or add a new currency:
Go to the file location-
\administrator\components\com_spproperty\models\fields\spcurrency.php
Please edit this as follows:
Duplicate an item and change value and text.

Here is the output:

This is all I can help with right now. Global currency changing may require different changes!
Note: Customization support is prohibited here.
Best Regards