Is there a way to change a session in progress? I started a workout, only to find it was way beyond me (“stand ups” are deceptively difficult, and 3x30 mountain climbers? I was destroyed after 10). Is there a way to mark an exercise as not done, or done for less reps? Or à way to replace it entirely? As it was, I was forced to quit the workout (losing my progress on the warmup and earlier exercises) to modify it.
Hey @b9999 
A big welcome to the community here at Freeletics 
Not really, but I think the absolute key thing you need to keep in mind is that at the end of your workout you have your chance to tell the Coach which exercises you struggled with, either because you couldn’t do them with the correct technique, or you couldn’t do all the reps assigned.
So, even if you can’t do a single rep of a particular exercise, you should still aim to complete the workout, and then indicate to the Coach through the Feedback screen the exercise or exercises that you struggled with.
Standups are actually incredibly difficult if done with the correct technique 
This brings me on to the next thing I want to tell you: if you can’t do a particular exercise, but there is an easier version, you should try to do the reps using an alternate. The Coach won’t tell you what these are, but you will quickly learn these. The really clear example, let’s say the Coach assigns you 10 Pushups which you can’t do, you could do 10 x Knee Pushups instead, giving you an easier version of the exercise to complete (working mostly the same muscle groups). You should still indicate to the Coach that you couldn’t do either some, or all, of the assigned reps. In your case here, you could have done Assisted Standups instead.
Finally do try and complete all the reps where possible, even if you have to take a short breather to break them up. For example, with the 30 x Mountain Climbers, you could break this up in to shorter sets of 10. Again, you have the ability to indicate to the Coach at the end of the workout, if there workout was too much (i.e. you needed excessive breaks).
I hope that’s clear-enjoy your future training!
