Yay! All done!
It was quite a bit of work and I looked into some easy automation to get copy the value "=[name]" into the Series cell of each post, but wasn't successful.
I did however find a method that sped up the process significantly.
At first, I would click the Series-cell of the post I was to edit, press F2 to make it editable and then go on with CTRL+V to paste in the value and then hit enter and go for the next row.
You can greatly speed this up by starting the same way, with clicking and then F2 and then go on with CTRL+V, but after this, you press Arrow down. This will make the next posts Series-cell editable, and you can go on with CTRL+V directly! And if you go Arrow down again you can paste yet again on the next post. With this method you can really hammer the keyboard and you get a lot more post done in the same amount of time.
It's still work, but the time you save can be cut by the factor of 20, or probably a lot more. Depending on how quick you are with your fingers
Thanks everyone again for the tips. I hope my little tip can come in handy for anyone wanting to do the same.