Hello Ivan, I put the update into my 4.12 with SAS ModAct 5.30 setup, not much other than that I can help with sorry to say.
I have been using this install for years to add anything new so I can see how it behaves, with this there seemed to be no issues as far as I can tell so far .
I have all my objects in their own folders outside of the Mapmods, there were not many to add in this case if memory serves, some indicate to have a 3do folder in there but I do not, just maps and textures.
I did not have a stand alone version of the EastBalt in my Mapmods so I was adding this new with no need to backup anything, textures added as you would any others, cannot remember if there was anything overwritten, I add so many things over the week it is a miracle this version of mine still runs.
I will download again just to follow the install steps again and report anything odd.
Wishing you all the very best, Pete.