Woodforde wherry

How strong would it make it if I added a kilo extra of sugar to a woodforde wherry kit

I’d be more concerned about it drying the beer out and lightening the body too much. I don’t know what the OG is for the kit but when I brewed my AG version, I aimed for 1.048. Adding another kilo is going to bump you up to around 1.064 and that’s not really what that beer is about. Your call though.