I took a little time out today and fixed this myself since I was wanting to use it as well.
So the first thing you want to do is create an "addons" folder inside of your project folder.
- So for example if your project is at "c:\shmup" create "c:\shmup\addons"
- Copy the "Resolution Switcher" folder from plugins into the new addon folder.
- Change the following few lines of code inside "res_switcher.gd"
Replace line #26
Next replace line #28
custom_window = preload("custom_res_popup.xml").instance()
custom_window = preload("res://addons/Resolution Switcher/custom_res_popup.xml").instance()
Replace lines 32-36
path = OS.get_data_dir()
var lpos = path.find_last("/")
path = path.substr(0,lpos)
lpos = path.find_last("/")
path = path.substr(0,lpos) + "/plugins/Resolution Switcher/list.txt"
path = "res://addons/Resolution Switcher/list.txt"
Now under your settings -> plugins you can activate Resolution Switcher as usual, have fun!
@vinod, if you like I can create a pull request for you, I have no idea if what i did here is best practice or not, but it worked for now!