You can edit Twine saves at https://mocha2007.github.io/tools/twine_save_editor.html . Be careful though, for example, if you change a character's gender, you have to also change the attraction of his partner or the game will error. If you change his name, you have to also change his name as listed in his partner's "bf/ gf/ partner" section, etc.
Definitely have a backup of your save.