Change the edge thickness in a graph plot

edit

I figured it out. The answer is do not use GraphPlot. Use GraphLatex. GraphLatex makes fairly nice 2D plots as tikzpicture with latex formatting on labels and lots of great customisations options. I would put a link to the docs but for some reason I don't have any Karma yet and cannot. For large, dense graphs it can be hard to view the whole thing on the default settings that view(H) gives you. In that case export the latex to a file and compile it in a minimal document with resizebox, e.g., as follows:

sage code:

H=graphs.CompleteGraph(100)
H.set_latex_options(
graphic_size=(200,200), #large value helps for large dense graphs
vertex_size=1,
edge_thickness=0.05,)
#view(H) #just display the latex graph in sage or in pdf viewer
with open('graph_tmp.tex','w') as f:
    f.write(latex(H))

latex document:

\documentclass{article}
\usepackage{tkz-graph}
\usepackage{savetrees}
\begin{document}
\resizebox{.9\textwidth}{.9\textwidth}{
  \input{graph_tmp}
}
\end{document}