It will vary from company to company most likely. I've added alloys to cars before and the insurance companies have either not increased the premium or have just told me to make sure there are locking wheel nuts on them.
As for window tinting, I'm not sure what that will mean. You can get the all rear windows tinted until they are totally blacked out but for the the front windows the maximum tint allowed is still very light. I read somewhere that some police forces now have a device that measures how much light passes through your window and if there isn't enough light then they could prosectue or at the very least tell you to take them off. Not sure how true that is.
As mentioned already best to ask your insurer before doing anything.