We would like to export a database from the website, modify it, for example change all keywords per listing in one go, and import the data again. This would save us a lot of work.
I installed a plugin to export the database in cvs format and the same plugin let you importing the database back. I was wondering if this is something that could be done and if there is anything we should be aware of before we even try.
Yes, this can be done with the advanced import/export plugins like WP All Import but in any case this would require manual mapping of listing fields, a third-party plugin would not recognize all the fields automatically.
and who could do a manual mapping of listing fields? Is this something I could do myself or should I ask a developer?
This depends on this third-party plugin features, as far as I know WP All Import plugin allows it, you can map the exported/imported columns to post meta fields. Coding skills are not required, you just have to enter the meta field names that correspond to the CSV file columns.