Right, enabling shunting seems to get me through the process of changing trains. Afterwards, I cannot get back to ETCS surveillance. No matter what I do, I get stopped for "runaway train movement" after entering all train data and trying to go through the signal; I can get going in SHP mode, but there is no block entry so I just get stuck in there, which is "fun" without track signage or any meaningful track maps. The scenario then proceeds to serve an almost impossible emergency stop, and after slipping through the red signal the train gets completely stuck. Also, it's not possible to save because, well, ETCS cannot be saved.
Guess I'll put this one back on the pile of shame and check back in a year, maybe it's become more accessible or something.