Can I add my own content to a purchased module?

I've had a look around the FAQs and other places but I cant seem to find an answer to this query:- I've been thinking about purchasing the Roll20 module Curse of Strahd to play with my players but I want to be able to add in my own battle maps for random encounters, some extra locations and NPC's, etc; basically, add in my own personal touches. I've been using Roll20 for years so I know how I would do it on a blank table, so expertise is not the issue here. Is this possible? 

Yes.  Once you create a Game based on a Module, you can change anything and everything about it.  It will be as if you uploaded all the content yourself.  One thing to be aware of though, is that once you remove something, you won't be able to get it back in that Game without shenanigans, so be sure you want to delete graphics and such before you do.  

Thanks for the reply - just what I was looking for! I don't tend to take away, just add to, so I would be unlikely to remove aspects but I will heed this warning!