Code contributions are most welcome. For any major edit (more than 15 lines, or so, in aggregate per person), you need to make a copyright assignment to the Free Software Foundation. This is necessary because the themes are part of the upstream Emacs distribution: the FSF must at all times be in a position to enforce the GNU General Public License.
Copyright assignment is a simple process. Check the request form below (please adapt it accordingly). You must write an email to the address mentioned in the form and then wait for the FSF to send you a legal agreement. Sign the document and file it back to them. This could all happen via email and take about a week. You are encouraged to go through this process. You only need to do it once. It will allow you to make contributions to Emacs in general.
Please email the following information to assign@gnu.org, and we will send you the assignment form for your past and future changes. Please use your full legal name (in ASCII characters) as the subject line of the message. REQUEST: SEND FORM FOR PAST AND FUTURE CHANGES [What is the name of the program or package you're contributing to?] GNU Emacs [Did you copy any files or text written by someone else in these changes? Even if that material is free software, we need to know about it.] Copied a few snippets from the same files I edited. Their author, Protesilaos Stavrou, has already assigned copyright to the Free Software Foundation. [Do you have an employer who might have a basis to claim to own your changes? Do you attend a school which might make such a claim?] [For the copyright registration, what country are you a citizen of?] [What year were you born?] [Please write your email address here.] [Please write your postal address here.] [Which files have you changed so far, and which new files have you written so far?]