You can do that, but not the way you wrote. You will have to use the text command and its subtleties, for instance Drawing Text in a Box.
You will need to get the 'XTick' values, not only to tell text what to write, but where to put the numbers. (You might also find strsplit helpful.) The section on Text Alignment will help you there. Remember to set 'XTickLabel',[] so they don’t display. Otherwise you will be competing with them. Also, assign ylim to a variable, and set the y-offset to your text call to -0.01 of the diff of that value to start, then adjust as necessary to achieve the result you want.
Here’s an example:
x = linspace(-2*pi,2*pi,250);
y = cos(x*0.25).*sin(10*x);
figure(1)
plot(x, y)
grid
xtk = get(gca,'XTick');
ymin = min(ylim);
yrng = diff(ylim);
set(gca,'XTickLAbel',[])
xlbl = strsplit(num2str(xtk,'%.1f '), ' ');
text(xtk, ymin-0.03*yrng*ones(size(xtk)), xlbl, 'HorizontalAlignment','center', 'VerticalAlignment','top', 'BackgroundColor', 'g')
I coloured the background green here because it otherwise doesn’t show up on the saved .png version:
