no you can not
It should not have water in it, especially if freezing weather is expected. Drain the pool to below skimmer line and drain the filter and filtration equipment.
drain some of the water out of the pool and replace with fresh water it would probably pay to work out how much to salty so you can work out how much water to drain.
Main drain sucks from bottom-as long as its under water its ok to run and have the returns just shoot water down into shallow pool.
Dilution. You would need to drain and replace some of the water in the pool.
Where is the drain located? If it is on the wall near the top then you can keep the water in the pool. If it is near the bottom then you may have to drain the pool.
If you mean you are losing water, it may be a broken or cracked main drain or possibly your hyrdo-static valve is malfunctioning. One other possibility is a break in the pipe going to the main drain.
If your pool is above ground it does not matter, But if your pool is in ground and you drain it it will act like a boat and float if the water table rises.
Unless you had the pool installed with a bottom drain there is not a drain on an above ground pool. You'll have to pump the water out using a sump pump or siphon it out using a garden hose. Please note having a bottom drain in any pool does not indicate that it is an actual drain as in house plumbing. The word "drain" or "main drain" is used most likely for lack of a better term. The only way to drain any pool is to use a portable pump and pump the water out. k
The valve for the main drain on older pools would be located at or on the equipment pad. You will most likely need a pool tech who knows how to plumb pool equipment to have it changed out. On the other hand if you mean replacing a broken or loose main drain grate then you would have to take the loose or broken grate to your local pool store for an updated version replacement. They will advise from there. k
If its not connected through the skimmer I imagine it's there to empty it. hmmm, on the above. The main drain in pools is for circulating the lower part of the pool and is not intended to drain the pool as in a bath tub.