Hi Raz,
parallel (manuall and automatic) processing is not supported out of the box. There is a customizing entry, saying if manual maintenance or automatic replication activated.
Table T77S0,
If you want to use first manual maintenance and then swich it to replication - you should pay attention to the number ranges. Manual entries will use internal SRM number range. By the replication the numbers are taken from HR System (if neccesary, mapping is possible on HR side). You should use different number ranges for your local HR objects and Replicated from ECC.
Best Regards
Konstantin