Alarm Evaluation for OPC Tags with Bad Quality

I have a UDT with many pre-defined members. Some of the members are not used on every instance, but they have an alarm attached to them. How will the alarm handle this? Will it just ignore the value and not evaluate the alarm, or will it always be in alarm? (the alarm is configured as an = 1 mode)

On a related note, what happens if I try to write to a disabled tag with system.tag.writeAsync()?