I often find myself wanting to add single exercises within a training day for my journey
Example 1. Wanting to do 30 min rowing in warmup then do suggested warmup in Freeletics
Example 2. Wanting to add core exercise after main training but before before doing cooldown.
Example 3. Wanting to search and add a a single exercise while I’m doing the training.
None of this is possible and I would either have to complete the full training warmup and cooldown before beginning new exercise.
This is not correct. Your example 2 is already doable. After completing whatever you are doing (warmup, exercise, workout, interval, cooldown), you are absolutely free to choose whatever you like from explore tab. You are not forced to complete your full coach day before adding more.
You are also free to row before warmup. 
Yes I’m able to leave the workout, start a new exercise but it then I won’t be able to go back to finish the cooldown that my coach gave me.
As soon as I leave the coach training it asks me if I’m sure I’m finished.
Which OS do you use and app version?
And what’s the steps to reproduce?
I really often leave the coach tab between the individual units (I don’t mean the rest between rounds of intervals or god’s), jumping around, doing other stuff from explore tab - was never asked if I really want to finish my coach day. Unless I clicked on the button to finish without doing all the units or I choose something from another coach day.
Thanks Mela, I checked today at training and you are correct. I could exit the training between exercises and go to Explore and begin a new exercise.
I think my feature request then boils down to this.
a) wanting to modify/create a training flow prior to starting it i.e adding in additional warmup’s (freeletics always have too short warmups) as well as adding in exercises between.
b) being able to more easily add exercises to the flow, whilst doing the training.