Is it possible to mine altcoin with antminer? Uh..I'm not sure if it's allowed to ask this kind of question here but anyway...

I saw some comments at other forum said that theoretically it's possible to use like antminer s9 from bitmain to mine other SHA-256 based altcoin, and I'm wondering how to do it practically.

There is a place for SD card on S9 so I was thinking will it be just like what we do to GPU miners. We download mining software from mining pool, save it to the SSD, and run it. 

So I checked those S9 set-up tutorial but it seems like I was wrong, there wasn't any step including download anything from mining pool.

Did anyone here try similar things before?  

And I know that this kind of ASIC miners are optimized for certain kind of coins. But for example, is S9 optimized for bitcoin or for SHA-256 algorithm?

Thanks a lot.
If an altcoin uses the SHA256 double hash algorithm for their proof of work algorithm, then yes, you can use antminers or any other Bitcoin mining hardware to mine those altcoins. You will need to modify the antminer in order to use other mining software (you should be able to ssh into it and load whichever mining software you want).