Hi,
Configuration package can update service period on signed service contract. Field validation has to be OFF like below setting.

As the error message indicates, the service period cannot be changed in a signed service contract. I feel that this specification is a bit too strict a restriction.
The service period defines the period of periodic inspection for preventive maintenance. I think it is no problem to realize the input error immediately after signing and correct it in the configuration package. However, after several regular preventive maintenance checks, it is better to make changes in the configuration package with sufficient verification because it may cause date inconsistencies.
I hope this will helps you.
S.Kawamura