Can I move my cable modem to a different room or do i need to contact Xfinity?
Yes, if you have an active cable coaxial outlet in the other room, you can move the modem yourself. If not, you'd need to get the coaxial connection moved/extended to the other room. If you have the expertise or know someone who does could add a new cable run inside your home. It doesn't have to be Comcast and Comcast doesn't need to know where the outlet is in your home. Of course, a bad connection could cause problems and you may end up contacting Comcast.
YES. You gotta arrange a similar/adequate signal on the coax connector on the wall in that other room however. Or you gotta run long cable to wherever the good connection is. Depending on your setup you may need a long RJ45-hardwire-ethernet wire too. If moving the cable-modem entails moving the wifi/hub/router too that may change your room-to-room wifi performance especially in large residence.