I was wondering what was the use of this Save as txt function in the Attributes Manager ?
The exported .txt file is quite clear and easily modifiable in Excel and for pens or surfaces for example, I can even see the RGB values which is pretty nice. But it seems that it only goes one way as there is no possibility to import that .txt file which would have been pretty handy.
You are correct. The TXT export is primarily for QA'ing your attributes.
If you want to do bulk edits to attributes in excel you have to export it to an XML file do some vodoo magic to get it into an excel format, make edits and then vodoo it back to the attribute xml format. There is no proper workflow for this.