Recently I have encountered 4 winter gates in Utah and Wyoming. They are typically only closed during hazardous snow conditions. But their current settings/tags prevent routing year round. Only Field is “Locked:unknown”. Only tags are “Name” and “Barrier:swing_gate”.
Apart from this behavior I would suggest access=yes + locked=no + locked:conditional=yes @ (snow) to describe this situation. Additional a short explanation for end users could be added in description.
Not the exact solution, but I think a good approximation.