Your probably should probably be declared as a $FEATURE knob, so search for that.
The perl script that parses param_info.in knows that something is a metaknob because the name begins with $. The code that uses metaknobs expects that they will be declared in the param_info.in as $<category>.<knob>. Where categories can be added arbitrarily, (but not discovered). So you should be reluctant to add new categories.
Metaknobs usually have multiline values, but this is not required.
As of 8.5.6 metaknobs can have arguments, which opens exciting new possibilities. see https://htcondor-wiki.cs.wisc.edu/index.cgi/tktview?tn=5739,0
For instance. The FEATURE : PerodicCronHook metaknob is declared thus:
from param_info.in
[$FEATURE.PeriodicCronHook]
friendly_name=Configure a Periodic Cron Hook, args: STARTD_CRON | SCHEDD_CRON , tag, period, exe [,hook_args]
default : @end
$(1)_JOBLIST=$($(1)_JOBLIST) $(2)
$(1)_$(2)_MODE=Periodic
$(1)_$(2)_PERIOD=$(3)
$(1)_$(2)_EXECUTABLE=$(4)
if $(5?)
$(1)_$(2)_ARGS=$(5)
endif
@end