Judging by the disassembled code, passing a zero should give you this output in the debug log
[LVAE] EP_SetMovieManualExposureMode() >> OFF
and passing any other value should give
[LVAE] EP_SetMovieManualExposureMode() >> ON
However, the explicit value you send does get stored at some struct at 0x16828, with an offset of 0x5C within that struct (so at 0x16884, if I understand the disassembled code correctly). Maybe that gets read somewhere else and it does matter what actual value you send (but I doubt it tbh).
There is also a EP_SetManualExposureMode function at 0xFF203C04 which takes a similar argument (did not find this in the stubs file at alins' repository. That file looks very incomplete(?), there are a couple more EP_* functions in that address range). Maybe that has some effect? It sets a value in the same struct, but at offset 0x58.
Giving it a 0 should log:
[LVAE] EP_SetManualExposureMode() >> OFF
anything else should give:
[LVAE] EP_SetManualExposureMode >> ON
(yes, without the parentheses
)