Hi psavola, thank you for all the explanations. That makes sense.
Unfortunately, I don't have a savegame from before the data seizure mission (also, I really would like to keep my messy but successful run of Morozova's hideout, which happened only a few days later).
But I still have a savegame from end of December, and I flirt with the idea of going back to that, removing 'STR_SYNDICATE_PISSED' from the discovered techs in the savegame. Then no retaliation and phase 2 missions will happen, since the mission generation scripts are executed only at the beginning of each month. I then continue the game, pretending that I did not do the data seizure mission before. I will do that mission again when I'm ready (in the sense that I have interceptors and Kitsune), which hopefully will set STR_SYNDICATE_PISSED again, triggering all that nasty stuff in the subsequent month.