Tonight I put this to the test and made an edited E84 .ssd removing 508 and adding 507 (pdc rear only). I then used this to default code my module with a blank FSW_PSW.MAN and though I lost the function of the PDC button, the module worked fine with the config and did ignore front sensor input. The only thing I didn't do was disconnect the front sensors. I then made a few changes to this via the NETTODAT.MAN file (as it now contains parameters for E92 sensor behaviour and positioning) and tested it again before reverting back to my previous config.
The critical changes from 8 transducers to 4 are ANZAHL_WANDLER, and (under Parkmaster) E84_HYSTERESE, E84_V_SCHWELLE_1, E84_V_SCHWELLE_2, E84_D_SCHWELLE_1, E84_D_SCHWELLE_2. All should be 4 channel.
This was my final test config running as 4 sensors, which worked with no issues if you care to try out a tested valid config.
https://mega.nz/file/PJgmCDoT#mf0RgQ...Hkzxj9jL-VTn3Q