Need to change the root certificate validity period

You can change the validity period in the \Windows\CAPolicy.inf
file on the root CA and then renew the root CA certificate. The renewed
certificate will then have the desired validity period. You'll still have
to distribute this new certificate otherwise all of your affiliated
customers will still have a copy of the old certificate with the old
validity period.

If \Windows\CAPolicy.inf doesn't exist, you can create them with this format:

[certsrv_server]
RenewalValidityPeriodUnits=5
RenewalValidityPeriod=years