I updated the test scenario, added 2 groups in which units added via group command on corresponding unit. One unit with use_group_distraction = true, and another with use_group_distraction = false. But all gruops still get distracted when get attacked. Is this still not a bug?
Updated scenario ...

When I use LuaCommandable:set_command with defines.distraction.none, when LuaCoomandable is UnitGroup, the units still get distracted when they are attacked. However, this does not happen when LuaCoomandable is Unit.
Here is the test scenario:

it would not be able to *enable* a replay on an existing save file

Yes, I know it. I'm starting my event from scenario with such command:
factorio.exe --start-server-load-scenario pvptorio-new/custom-pvp --server-settings .\server-settings.json --port 34197
And if I want to enable replay, I ...

TL;DR
In version 2.0.52, the --run-replay command line option was added, maybe this is a good reason to finally add the function to enable replay recording from the command line?

What?
I suggest to add command line option to enable replay recording. Something like --enable-replay or additional ...