pre-abbrev-expand-hook

pre-abbrev-expand-hook is a variable defined in `abbrev.el'.
Its value is

nil

• This variable is obsolete since 23.1;
  use `abbrev-expand-function' instead.
• This variable may be risky if used as a file-local variable.

Documentation:
Function or functions to be called before abbrev expansion is done.
This is the first thing that `expand-abbrev' does, and so this may change
the current abbrev table before abbrev lookup happens.

You can customize this variable.