Resolution and Issues With Monitor

In terms of Gameplay, are we allowed to change the resolution of the actual game like the current maplestory? I don't think this changes the gameplay experiences but enhances it. I have a 4k monitor and almost everytime I change to 800 X 600 or back to 4k, it cuts half of my screen off. This could be a displayport issue (although my cable supports higher resolutions @ 60 Hz then my monitor and so does my gtx 970. The scrappy HDMI cable only supports 4k @ 30 Hz. I play more then just maple on my pc for > 30 Hz. It really only happens a LOT when switching to a lower resolution or back to a higher resolution. The only way to fix it, is to manually turn my monitor off and then turn it back on. Sometimes half of my screen flashes (with a bunch of different colored pixels randomly), and the other times it remains completely black. It seems I have to keep it off for at least a few seconds before I turn my monitor back on and that fixes the problem. Sometimes I have to do this 2-3 times because it seems I went too fast.