Differentialequations.jl - modify `u` in `f` possible without callback?

I don’t think there’s any integrator that supports that, in any language, even at a mathematical level. It doesn’t quite make sense because time doesn’t always go forwards: what if a step is rejected? This is one of the quintessential cases for using a DiscreteCallback: use PresetTimeCallback at 2.0 to do this change.