So, i made a mod with data.lua containing this:

data.raw["unit"]["small-biter"].movement_speed = 0.01
data.raw["unit"]["small-spitter"].movement_speed = 0.01

data.raw["unit"]["small-biter"].ai_settings.allow_try_return_to_spawner = false
data.raw["unit"]["medium-biter"].ai_settings.allow_try ...

Thanks for answer, i could not find how i can access 'allow...' variable. I just not familiar with Factorio modding staff, never used it before.
So, all this means i need to create mod for changing this setting for this scenario?
In data.lua write something like that?:

data.raw["unit"].ai ...

I downloaded this scenario (https://forums.factorio.com/viewtopic.php?f=36&t=85746), played a bit and get that issue - spitters disappears after some time. I tried to modify control.lua file of scenario, adding there "allow_try_return_to_spawner = false":

local handler = require("event_handler ...