Do I need developer access to do this?

Hello, 

I am currently trying to make changes on a css file of and old content type ("Audio") that I found in moodle 3.9. The problem occurs when I try to upload the .h5p with the modification on the css file, some message appears idicating I am unable to to that and even when I upload the .h5p package without any modifications, I am still not able to upload this to moodle or even to h5p.org

I read the "About developer access" post (https://h5p.org/node/59) and I think that I need developer access the make any changes to the files of any content, but I am not sure about that because I read some other posts in the forum saying that in the end it is all open source so I am confused