I booked Singapore airline to HKG for $1200 departing on 26 January, but I now notice that fare will be down to $330 in mid-February.
If I change the date and pay the administration fee of $250, will I be able to get the difference of the price of the ticket less the admin fee?
Not sure if you meant Singapore Airlines specifically (in which case maybe), but worth noting on other airlines, you absolutely can change flight to a cheaper fare and get refunded the credit (albeit as eCredit).
Also many airlines have no change fees like Delta.
But both those are subject to the tickets T&Cs and class so OP needs to check theirs before asking others.
Have you read the Terms and Conditions of the ticket you've booked? That'll tell you if the ticket is refundable or if there's any fees for changes.
I think OP already knows there is a $250 fee for changes. Just wants to know if you get the fare difference when changing to a lower priced fare.
It really depends on the fare class and type of what OP has booked. Some are just non-refundable.
No
No. Pretty much all airfares need to be changed to an airfare of equal or higher value whilst also paying the change fee.
The only option would be to cancel (provided there is a small cancellation fee, which I doubt) and rebook the lower fare.