If I remember correctly that is a compiler error, because Foo is not initialized, so no boom.

But if you still want to get your point through and have a boom.

  MODULE Boom;
  IMPORT SYSTEM;

  VAR Foo : POINTER TO INTEGER;

  BEGIN
    Foo := SYSTEM.CAST(POINTER TO INTEGER, 43414);
    Foo^ := 123;
  END Boom.

Notice the use of IMPORT SYSTEM and SYSTEM.CAST, explicit, easy to search for, and to forbid via compiler switch (no unsafe code).