You might get a message that the savegame will be missing files. That's just because I use True Storms and a few texture mods. Loading the save anyway shouldn't have any detrimental gameplay effects. The texture mods aren't even related to the player character or NPC skins or anything like that. They're basically Optimized Vanilla textures.
There's a clean laundered dress pretty close to Sanctuary in a nearby shack. It's not the right color, but if you really want something a bit closer to Pam's outfit, the closest I've seen so far is the ratty skirt that you can find in Diamond City.
To install, just unzip the save file into your Fallout4 saves folder. For me, that folder is in my documents folder/my games/fallout4/saves.