Simostools or VW_Flash.
Reprogramming a spare ECU requires boot mode, because OBD/UDS programming isn’t possible unless the immo is released.
https://github.com/bri3d/TC1971_CAN_BSL or a big commercial tool (bFlash, AT, MMS, etc) for this (the ECU needs to be opened).
The ECU is a slave unit in immo, not a master, so key enrollment won’t be affected.
Simos 18.2 is basically the same thing as Simos 18.1/6 with some slight pinout differences. It shares the same SC8 project type so reflashing is the same.