You will need to use the ExportTool pack, and extract the save games to a format that is readable in a text editor, and manually search through the file to find the area to edit/add tags.
I tried that.
I can use ExportTool and convert LSV file to two LSF files and then make changes in my save but ExportTool is not able transfer LSF files back to LSV and if I try start load save game with LSF files, game crash.
Are you referring to a save game editor? If so, I don't think you're in the right forum for that, as it isn't really modding.
I could not find any mention of something like "save game editor" but people have already begun to create mods that are able to add new skills or tags and I thought that these people use programs that could help me with my problem.
So in a sense it's a question about modding.