ATC - MSFS 2020 - Microsoft Flight Simulator - SU14 - KHPN to KIAD
ATC Enforce Flight Plan option should be OFF for ATC to be able to direct you to another runway because of weather etc... It is located in the User Experience area in Assistance area.
SU14 MSFS added an option to turn On or Off so that ATC in the game can direct you to a runway based on weather, wind, etc... Depending on whether the option is On or Off. Explained in this video to help you.
It does indeed work as I turned it ON and set runway 01R as my runway and it vectored me into 01R instead of the normal 19L apparently or it could change with the option OFF, depending on weather, wind, etc...nice!