I joine the imperials after joining the stormcloaks and then canning that save. My question is, when under the stormcloaks, after taking Windelm the non-nords complained of discrimination. When you take the other holds as a stormcloaks are all the non nords upset? And all the Ulfric supported Jarls end up in his castle after being ousted.... Where do te imperial supporting Jarls end up after their cities are sacked by stormcloaks???
There is some dialogue and the guards will change to Stormcloaks, but other than that, the impact is minimal. Oh and some of them have new jarls in place. Some shopkeepers do complain, like Arianne Avenicci says that she'd have been run out of there if she wasn't married to Uthgerd.
The imperial jarls are all in the basemant of the Blue Palace and they will give you an earful. lol The most bitter seems to be Balgruuf, who repeatedly makes threats against Ulfric's life, which makes me respect him for courage even though it doesn't seem like the healthiest course.