Take a screenshot with Print Scr and paste the picture into Paint (Or any of your graphic program of choice.)
Recolour the background. (If you don't mind the yellow, just skip this then)
Crop it to size and reupload it to an imagehosting site. (Photobucket etc)
Link it using the custom avatar function in GitP.
EDIT: Also, I finished revising the crazyLyra fic. It should be gold now, barring grammar-ninja edits and stuff. I did think I made it about 20% more insane with the ending, but I felt it was appropriate.
My thanks to all the bronies in this thread. The special friendly crazy that permeates these pony threads was an inspiration.
Spoiler(Special thanks to Thanqol for his remarkable insight into insanity. I apologise I can't incorporate more of your ideas into the fic, as I feel I can't do justice to them. Also, you can't get enough Phoesauce for this. )
Without further ado. Lyra Crazy. Now about 20% more crazy.