You should be able to modify any WordPress theme purchased from anywhere. It does not depend on licensing. But you have to use a child theme for that and you should never edit theme core files as you will loose all your changes once you update the theme in the future. All of my themes are child theme ready, so you are able to modify them to your needs as you please :)
Just a side note, I’m not sure how other themes can be encrypted as they are using CSS and PHP and HTML code which can not be encrypted in WordPress in any way as far as I know. But to answer your question, yes all the code in Angelica is accessible, readable.