Am 21.04.17 um 18:52 schrieb Jonathan Fine:
> With David's correction, do the LaTeX experts here see any fundamental
> reason why this would not work?

it is more or less what babel does (only after begin document), the 
point is not that it is difficult to solve his particular problem, for 
which is is enough to move the definition or to make < active before it 
or ... the problem I was pointing out is the difficulty of a general 
interface solution that works out of the box.

Again as such that is not impossible at all, but is much more than an 
adhoc fix, as I said, there are reasons why babel delays making things 
active and those reasons need to be taken into account for a general 
solution.

frank