It might come the time where you need to change the validity period from SSL certificates issues by your Windows CA. Changing that required some changes to the CA itself at first.
So the first step would be to check what is the current settings via:
certutil -getreg ca\ValidityPeriod
certutil -getreg ca\ValidityPeriodUnits
If you wish to change that then to 10 years use the following:
certutil –setreg ca\ValidityPeriod Years
certutil -setreg ca\ValidityPeriodUnits 10
After that your certificates can be issues (via the certificate template) up to 10 years.