LDAP Import does not import changes into current groups of the school year but creates new ones.
If you create a new school year and assign the groups to it, the groups will be completely recreated with the next LDAP import or when an LDAP user logs in. So you can not sycnen correctly changes that happen in the school year.
Can you build a script as a workaround that syncs the changes from the new groups to the school year groups?