As to the liability issue, they will be covered by whatever they were covered with before so long as the rule allowing metal cleats is in writing by the league.
The reason I phrased it that way, if this is a HS league and the umpires are registered only with ASA, and the teams are not registered ASA, I'm not sure they were ever covered. Merely using ASA rules doesn't do anything wrt insurance
AFAIK.