To quote myself from another thread:
To be honest, the million different combinations of engine modes are stupid. The FIA just needs to be strong with the teams and say "you can have 5 engine modes. No more, no less". Let the teams declare what those modes are to the scrutineers at the beginning of the season like the gear ratios and be done with it.
It seems like an odd decision to change this mid-season, but we'll see what happens to Mercedes in Q2 at Spa. That's when they always turn it up and suddenly go a second faster than anyone else on the medium tyres too, so if that doesn't happen and the others are closer, we'll know it has actually had an effect.