I would like to hear other people's experience with tonglen practice for people who have harmed you in some way. I find this very helpful. I do it at work and and I'm having compassion where I once had none.
I've found this practice very helpful as well in dealing with disagreeable people (ie. those that piss me off
The way I learned it is to practice it for loved ones or friends (agreeable folks) first, secondly for strangers (neutral people), and lastly and finally for enemies or people we dislike (disagreeable).
It can really help break through that attachment which makes us cling so tightly and ultimately leads to us thinking we are entitled or even superior. After all, when we experience the ripening of bad karma, it is us, ourselves, who created that karma in the past.
It can lead to compassion in such circumstances. It's value is immense.
Not only that but it helps to create a huge amount of merits. The bodhicitta motivation is the most supreme motivation.
I am glad to see you have benefited from the practice.
All the best,