Yes, it is possible to modify the size of the partitions on Edison. Please check this guide on how to do it http://alextgalileo.altervista.org/blog/changing-partition-setup-edison/. Debian is not officially supported but some users have done it. Take a look at these links, you might find them useful https://communities.intel.com/thread/55498, https://communities.intel.com/message/259745#259745. Let me know if this is what you are looking for.