Suppose that i have a figure
fig = figure,
ax = axes(fig);
rng(2017)
plot(ax,rand(1,10))
Now i dont know what is my data
Suppose that i have just the figure, let us extract data from figure
Line_Obj = findobj(gca,'Type','Line')
X = Line_Obj.XData;
Y = Line_Obj.YData;
Now i add an offset in it
hold on,plot(gca,X,Y+0.5)
Remember that this demonstration is for Line object, if your plot contains any other object like scatter, histrogram etc, you have to change it in findobj
Edit:
if you dont want to plot it, just use copyobj for that purpose
h = copyobj(Line_Obj,gca);
h.Color = 'g';
h.YData = h.YData-0.4;