Adding custom fields to a package

I am using onespan for sending documents for signing.
Is there a way to add custom fields while creating a package? 
When i am sending the mail for people to sign the document, i make use of fields such as $PACKAGE_NAME and $PACKAGE_OWNER_EMAIL in my html file.
Let's say i am an admin of my app and i send the documents via mail to be signed to users 
Is there a way to add details like my name and my organisation name and other custom details in the package and if so, how do i use that in my html file 
For example, let's say i want to add a field called documentCreator, what would be the way to add it in the package and how to use it in the html file 


Secondly, In a usual html file, the concept of handlebars are used for writing conditions and modifying the content of the file based on the conditions, 
Is there a way to do so in onespan like if based on my $PACKAGE_OWNER_EMAIL, i want to change the content of my html file, how do i do it?

Thanks and Regards,
Rahul