Creating a custom index.html for new subdomains
Since there is no template for the subdomain index.html (will likely change), you can still create your own index.html files for them, but you have to use the subdomain_create_post.sh file.
In it, put something like:
rm -f $INDEX
cp /your/custom/index.html $INDEX
chown $username:$username $INDEX
Then chmod the subdomain_create_post.sh to 755.
Obviosly, change /your/custom/index.html
to whatever you'd like.