How to change the plotstyle in mathematica?

[KFC]

I am running some notebook, developed by someone else, in mathematica. One of the function defined in the notebook will show a graph. Since the notebook is kinda messy and I don't want to modify it. To alter the title and/or style of the graph, I try the following

G = ShowMapping[2.3];
Show[G, PlotLabel->"Some title"];

This works great. But when I try the same way to alter the plot style, it doesn't work

Show[G, PlotStyle->{Thick}];

Any idea to alter the plot style in this case? Thanks

 

[djelovin]

It is not very elegant, but you can use:

ToExpression[
ToString[Insert[InputForm[G], Thickness[0.02], {{1, 1, 1, 3, 1}}]]]