is it possible to edit ble_central code and make it behave as both central and peripheral in S120
No. The S120 is a central only, the S130 is able to be central and peripheral.
ok is that sure??
S120 2.x.x can choose role during SoftDevice enable, so it supports both roles, but not at the same time. The intended use for this is to start up as a peripheral for e.g. DFU, since the throughput is much greater for the peripheral.
