For your !alert test, you have to run the right command for the vars to be expanded.

mzscript (!varset): !msgbox %{target} or !exec !alert %{target}
step.rc (var value): !alert $target$
xlabel (!setevar): !parseevars !alert %#target%#

If you're using !varset for your target var, then you'd do !setevar panicbuttontooltip "%{target}\asd"

Also note: In mzscripts, !parseevars isn't required for %#vars%#.