I checked, that in Pharo image i could simply use:

foo_bar

	a_b := 5.
	FOO_BAR := 10.
	
	^ FOO_BAR

and it works!

It would be cool to have similar in squeak, even if it may require to
define something like:

MyClass class>>canIHasUnderscores
  ^ true

It would be really nice to have, especially for things like OpenGL
API, which using underscores in constant names.
Exterminating underscores in those identifiers makes them really hard
to read , and awkward to use, because
every time you going to code something, first you usually refer to
docs, where you see these names with underscores,
but then once you going to type this name it costs you an additional
mental effort - don't forget to skip underscores.

-- 
Best regards,
Igor Stasenko AKA sig.