Change default application for some files

I would like to associate Adobe Reader with a folder & its subfolders (>500 files!) and leave all other pdf files to open with another app (Skim or Preview). There are way too many files for me to be willing to change each file manually & the 'Get Info' dialog only seems to be able to change 1 file or all files. Does anyone know a way to change the default app for files in folder: /users/Gandalf99/FolderToChange without changing the systemwide default?

I bet there's a way to do it in Terminal by specifying the folder. I'm not sure if you can goggle something like that to get the exact command. But you'd think there would be a Unix tutorial online somewhere, and maybe even a Mac OSX Terminal tutorial.

There might be some arcane terminal command somewhere, but I doubt it.

Wouldn't it be a LOT easier to just put the Adobe reader in your dock and when you want to read documents from this one folder just drag the ones you want onto Reader's icon?