This mod provides you with a fully customizable kill feed. Every setting can be changed in the mod options menu.
Note: You can copy one of the killtext files in the data directory to the mods/saves directory, rename it to "killtexts.txt" and edit it to your liking (so you won't lose it on a mod update). You can also swap the kill icon to a custom image by placing an image file named "kill_feed_icon" in mods/saves, supported filetypes are png, dds and texture.
You can also find this mod on GitHub, so if you want to help with anything, feel free to fork the project, make changes and create a pull request when you're done.