If you want to edit the vanilla textures or keep a backup of the classic look, you need the source files.
If you want to tweak the vanilla textures yourself: vanilla texture pack
The "Jappa-esque" RefinementSince the 1.14 "Texture Update," many creators have focused on matching the style of Jappa (Minecraft’s lead artist). These packs extend that soft, painterly style to modded items or older blocks that haven't been updated in years. How to Choose the Right Pack for You If you want to edit the vanilla textures