You can't do it directly with
gpg. The code which is compiled to make
gpg supports certain command line options, and some of those have aliases, but it's not something you change directly.
You could write a script/wrapper for
gpg (say, call it
my-gpg) which took one set of command line options and then converted them into the options
So you could write the script, and then use,
my-gpg -c -g AES25
and the script would in turn run
gpg -c -cipher-algo AES25
But you'd need to implement that yourself. You could use a simple bash alias to achieve the same thing as well.