The only public service that allows for modified ham gear is MARS.
MARS stations are separately licensed and communicate with
MARS stations, or regular hams under their ham license.
IF the radio does not have 60M that can be done legally.
The question becomes can the radio do that without
extensive or difficult mods.
There is SHARES, as part of CISA.gov. to participate you have to
be part of a group that has emergency services stake. How to
participate seems complex and very rule bound. Unclear what
radios can be used or how. from first pass read its not a hack
a radio and drop in thing, its a fully coordinated activity.
All others. FRS, GMRS, MURS, CB, any block owned by
the military, police, Fire service, Aviation, are all prohibited
except in the use in an emergency where no other means
of communications is possible. For nominal service use the
radio must be type accepted for that and the license holder
for the service must be able to accomodate one more radio.
That is why you hit a brick wall.
Allison