How to change thickness of a single in line in EXISTING plot - plot

Question

I create a plot with many (50+) lines on it.
I would like to set up a keybind such that I can toggle through each line and change it's thickness, and so making that line stand-out from the rest, then when I press the key again, the next line becomes thicker.
That way I can examine each line clearly, next to the others.
I know how to assign keys, but I don't know how to change the thickness of an exiting line on an existing plot.
How can I go about this?
Moon
EDIT 1
Is it possible to do something like this:
set style line 1 lt 2 lc rgb "red" lw 3
set style line 2 lt 2 lc rgb "orange" lw 2
set style line 3 lt 2 lc rgb "yellow" lw 3
set style line 4 lt 2 lc rgb "green" lw
savedls1 = ls 1
savedls2 = ls 2
savedls3 = ls 3
savedls4 = ls 4
plot <whatever> ls 2 #Original style
set style line 2 lt 2 lc rgb "black" lw 2 #new temp style
plot <whatever> ls 2; replot #Temp new style
set style line 2 savedls2
plot <whatever> ls 2; replot #Back to original style

Answer 1

In the command line (v4.6 patchlevel 3), you can do it like this:
Specify a line style:
set style line 1 lt 2 lw 2 pt 3 ps 0.5
When plotting, specify this line style:
plot sin(x) ls 1
Now, you can change this line style, e.g. changing the line width:
set style line 1 lt 2 lw 4 pt 3 ps 0.5
A simple replot will produce the same graph with the updated line style.
EDIT
Christoph provided this information in a comment, addressing the question of a key-bind:
It is enough in step 3 to change the linewidth, the rest remains unchanged:
set style line 1 lw 4
That would allow you to define two different linewidths and toggle between them:
lw_small = 2
lw_thick = 5
set style line 1 lt 2 lw lw_small pt 3 ps 0.5
plot sin(x) ls 1
set style line 1 lw lw_thick # here, everything but the line-width stays constant
pause 3
replot
set style line 1 lw lw_small
pause 3
replot