Will it harm an imr battery cell to be removed from the charger, in the middle of a charging cycle and then discharge it again
Not at all. In fact, it could actually lengthen the life of the battery.
Li-Ion
batteries hate being below a certain voltage, usually somewhere under 3.0V. And the higher the voltage above that, the faster the battery ages or degrades. So by not allowing to charge up to a higher voltage you can actually extend the life of your battery...a tiny, truly tiny bit. That's why, if you're not going to use a battery for a few days or longer, it's better to leave it half-charged rather than fully charging it up.
There is an argument to be made for not using it directly off the charger though. Especially if it was a fast charge that got the battery warm. Allowing the battery to cool completely to room temperature should prevent any problems. Though some say to leave it for a few hours before using again. I don't have enough information to say whether waiting beyond the point that the battery reaches room temp makes a difference or not.