From which version of OF this kind of mappings works?
Map file:
1=ON
0=OFF
=Unidentified
I’ll form my question differently… 
Is this change included in OH 2.4 version? I can’t find percise release date of 2.4. Articles found suggest that yes (it was something near 17 Dec 2018), this version should contain it, but for me it doesn’t work:
2019-04-10 13:15:49.664 [ERROR] [ntime.internal.engine.RuleEngineImpl] - Rule 'Lawn moisture': Could not cast 0.28 to org.eclipse.smarthome.core.library.types.QuantityType; line 1480, column 9, length 49
Map file:
0=Measurement error!
=OK
I think you need to use OH 2.5 M1. I can confirm that it works there.
I’m using docker, so I’m wondering should I use version 2.5 SNAPSHOT already? I’m still stabilising my OH configuration,so is it safe?
Will my config (bindings) be preserved? What could breake?
Is there some kind of safe procedure?
Use openhab/openhab:milestone for the latest milestone build. I’d stay away from the SNAPSHOTS for the time being until all the problems caused by merging ESH back into OH and the build system get worked out.
Especially with Docker, changing versions is safe. Your bindings and configs will be preserved. The Container will take a backup of everything automatically when you change versions so you will be able to go back should you need to. I never have and I’ve been running Docker with a newly created Container about once a day and a new version of OH usually once a month.
If you want to be very safe, make a backup of all the folders you mount into OH or your data container. Then just pull the milestone tagged image and run the container per usual.