http://reference.wolfram.com/mathematica/ref/Files/BarLegend.en/I_70.gif
The code in the link as well as documentation of BarLegend may be helpful in customising bar legend. Look at Contours option.
I was overly optimistic, however,
ListDensityPlot[
Table[ArcTan[Cos[x + y], Sin[x + y]], {x, 0, 10, 0.01}, {y, 0, 1.2,
0.01}], DataRange -> {{0, 10}, {0, 1.2}},
PlotLegends ->
Placed[BarLegend[Automatic, {-2, -1, -0.5, 0, 0.5, 1, 2},
LegendMarkerSize -> 250,
LegendFunction -> (Framed[#, RoundingRadius -> 5] &),
LegendLabel -> "z-value"], {After, Top}], ColorFunction -> Hue]
is partially successful. The ticks for -1, 1 are not displayed. The LabelStyle option does not work but perhaps this is a start.

EDIT
Manipulate[
ListDensityPlot[
Table[ArcTan[Cos[x + y], Sin[x + y]], {x, 0, 10, 0.01}, {y, 0, 1.2,
0.01}], DataRange -> {{0, 10}, {0, 1.2}},
PlotLegends ->
Placed[BarLegend[Automatic, p, LegendMarkerSize -> 250], Bottom],
ColorFunction ->
Hue], {p, {{-2, -1, -0.5, 0, 0.5, 1, 2}, {-Pi/2, Pi/2}, {-1, 0,
1}, {-0.3, 0, 0.7}}}]
The above runs slowly on my old machine. However, illustrates the capacity to change tick labels with the caveat that sometimes not all specified contours are given a tick label.
Further Dynamic@p
does not work as a way to speed up processing. Note {-Pi/2,Pi/2} is presented at 3 decimal places.

An example snapshot follows.