Disclaimer: If you have ANY doubts about modifying your game files, then DO NOT do anything to them. I am not responsible if moving these files breaks your PC, game or account.

I am not associated with or endorsed by Mihoyo. And yes, they know about this video, because I sent it to them. See the pinned comment below.

Basically, if you want the energetic, pre 1.3 Barbara voice back, just go into your Genshin Impact game's folder (where you have it installed on your PC) and from there it's (whatever hard drive you have the game installed) \Genshin Impact\Genshin Impact Game\GenshinImpact_Data\StreamingAssets\Audio\GeneratedSoundBanks\Windows\English(US)

BACK UP ALL THE PCK FILES INTO ANOTHER FOLDER FIRST.
You can just create a new folder in the "English(US)" folder.

Just move the files with the name "VO_1.3_0.pck" in them to another folder. That'd be "VO_1.3_0.pck" to "VO_1.3_7.pck"

Warning: Characters that were introduced during the 1.3 updates will lose their English voices, and all 1.3 story missions will stop playing voice lines during cutscenes. This affects Hu Tao, Xiao, and possibly others. You can reverse this by putting the above VO PCK files back into their proper folder.

Note also that these changes only affect the YOUR game, and will have no effect on other players.

To Mihoyo: Please do not remove the Pre 1.3 English Barbara files from the game. Some of us prefer her old voice to the updated voice.