Is it possible to override git command by git alias?

FWIW, I solved this (okay, "worked around it"...) by writing the following ~/bin/git wrapper, which checks for, e.g., ~/bin/git-clone, and calls that instead of the built-in.

[NOTE: I apologize for any "clever" bash-isms, but after you get past the two helper functions — one to expand symlinks and one to search your $PATH for the executable being wrapped — the actual script itself is just Three Lines of Code™... So I guess I'm not sorry after all, hehe!]

#!/usr/bin/env bash

###########################
###  UTILITY FUNCTIONS  ###  ...from my .bashrc
###########################
#
# deref "/path/with/links/to/symlink"
#   - Returns physical path for specified target
#
# __SUPER__
#   - Returns next "$0" in $PATH (that isn't me, or a symlink to me...)

deref() {
  ( # Wrap 'cd's in a sub-shell
    local target="$1"
    local counter=0

    # If the argument itself is a link [to a link, to a link...]
    # NOTE: readlink(1) is not defined by POSIX, but has been shown to
    #  work on at least MacOS X, CentOS, Ubuntu, openSUSE, and OpenBSD
    while [[ -L "$target" ]]; do
        [[ $((++counter)) -ge 30 ]] && return 1
        cd "${target%/*}"; target="$(readlink "$target")"
    done

    # Expand parent directory hierarchy
    cd "${target%/*}" 2>/dev/null \
      && echo "$(pwd -P)/${target##*/}" \
      || echo "$([[ $target != /* ]] && echo "$(pwd -P)/")$target"
  )
}

__SUPER__() {
  local cmd="${1:-${0##*/}}"
  local me="$(deref "$0")"

  # NOTE: We only consider symlinks...  We could check for hardlinks by
  #       comparing device+inode, but stat(1) has portability problems

  local IFS=":"
  for d in $PATH; do
    [[ -x "$d/$cmd" ]] && [[ "$(deref "$d/$cmd")" != "$me" ]] \
      && { echo "$d/$cmd"; return; }
  done

  # else...
  return 1
}

########################################################################

# (1) First, figure out which '$0' we *WOULD* have run...

GIT="$(__SUPER__)" || { echo "${0##*/}: command not found" >&2; exit 1; }

# (2) If we have a "~/bin/git-${command}" wrapper, then
#     prepend '.../libexec/git-core' to $PATH and run it

[[ -f "${HOME}/bin/git-$1" ]] &&
  PATH="$PATH:$( "$GIT" --exec-path )" \
    exec "${HOME}/bin/git-$1" "${@:2}"

# (3) Else fall back to the regular 'git'

exec "$GIT" "$@"