First of all, thank you so much for your help !
I really like your suggestion and I have tried it but I am not sure that, this is what I was expecting.
I may be wrong but in your example, my accounts will be available within two sub-branches (ou=local or ou=msad), even if they are available via "dc=example,dc=com".
Due to my LDAP client "pGina" where I can only configure one Group DN Pattern (e.g. : cn=%g,dc=example,dc=com), I shall have all users and groups within "dc=example,dc=com".
What I expect is : cn=userlocal,dc=example,dc=com instead of cn=userlocal,ou=local,dc=example,dc=com cn=userAD,dc=example,dc=com instead of cn=userAD,ou=msad,dc=example,dc=com
I had chosen slapd-meta in order to rewrite the suffix name of all the entries.
Best regards, Alexis