Hello Elisa,
If you have an article linked to tag A and you want to replace tag A to be replaced with tag B that won't be possible with current import settings. With the attached patch file, i have added an option Append tags Yes/No on Options tab in template settings. If set to Yes, the tags in the import file are appended with existing tags of article. If set to No, existing tags will be deleted and new tags will be linked to the article from import file. Your issue will be solved if you set Append tags option set to No.
Load the patch file, run the import and let me know on how it goes.
Kind regards,
Tharuna
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