It is not, because as others have pointed out, the behavior in question is shell-dependent. As you (the OP) have pointed out, this is a bit of a pedantic, maybe even humorous?, sort of topic.
However, on GNU systems, your initial premise has another solution available: cp --no-preserve=all file1 file2. Try this out, I think it will satisfy your described situation (e.g. modifying contents of file2 while not modifying its attributes).
Example:
$ ls -l
total 8
-rw-r--r-- 1 tniles sambashare 16 Dec 16 12:21 fezzik
-rw-r--r-- 1 tniles tniles 14 Dec 16 12:16 fred
$ cat *
Lookout, world!
Hello, world!
$ cp --no-preserve=all fred fezzik
$ ls -l
total 8
-rw-r--r-- 1 tniles sambashare 14 Dec 16 12:22 fezzik
-rw-r--r-- 1 tniles tniles 14 Dec 16 12:16 fred
$ cat *
Hello, world!
Hello, world!
UPDATE
Actually, I just noticed that my system's cp by itself seems to preserve attributes unless -a or -p are specified. I'm using bash shell and GNU coreutils. I guess you learn something new everyday...
Test results (by Wildcard) including hard link and different permissions:
$ ls -li
total 12
913966 -rw-rw-r-- 1 vagrant vagrant 30 Dec 16 20:26 file1
913965 -rwxrw---- 2 pete vagrant 39 Dec 16 20:35 file2
913965 -rwxrw---- 2 pete vagrant 39 Dec 16 20:35 hardlinktofile2
$ cat file1
This is the contents of file1
$ cat file2
This is the original contents of file2
$ cp file1 file2
$ ls -li
total 12
913966 -rw-rw-r-- 1 vagrant vagrant 30 Dec 16 20:26 file1
913965 -rwxrw---- 2 pete vagrant 30 Dec 16 20:37 file2
913965 -rwxrw---- 2 pete vagrant 30 Dec 16 20:37 hardlinktofile2
$ cat file1
This is the contents of file1
$ cat file2
This is the contents of file1
$
