SQL Server Replication changing a tables ID numbers
You need to turn no 'NOT FOR REPLICATION' on the field, then the target will take the identity field from the source table rather than trying to generate its own

this can be done by:

alter table dbo.testtable
alter column [id] add NOT FOR REPLICATION


NOTE, I'm not sure what doing this while replication is enabled will do, if you do enable it while replication is on, ensure your replicate schema changes setting is on for that publication