I will give that a go.
Tried using TWRP and failed. Going for manual via TWRP file manager.
The following is my observation :
1. Flash TWRP via Mobile Odin lite
2. Flash deodex
3. Flash SU
Confirm at this point that odex files are gone.
4. Boot to system, and update build.prop with qemu.hw.mainkeys=0
5. Flash v2 via TWRP
6. Attempted to match contents of v2 zip with permission folder, but do not see the expected files.
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I managed to get multiwindow as you have guided.
The following are the details that might help others:
1. Using MD3 stock (did not perform factory reset)
2. Flash TWRP recovery using Odin
3. Deodex (TWRP)
4. Root
5. Update build.prop as per OP
6. Used ES Explorer to extract v2 zip into /SdCard/0 directory as TWRP seems to not see below SdCard
7. Boot to TWRP
8. Mount "system"
9. Advanced > File Manager
10. Copied "system" folder into /
11. Navigate to /system/etc/permissions and chmod com.sec.feature.multiwindow.tablet.xml to 644
12. Reboot to system, Settings > Display and you will see the multiwindow option.
Actually, you will notice inverting of colours, as some said that it is due to Note8.
Have to re-read the forum to fix Splanner. And seems like the windows are floating. Might try v4 using same method. Will update again.
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