No, I wouldn't put it in an import module. A BEGIN block would be better. If you put it in import, you have no guarantee that the import method will ever actually be called. It's quite easy to load a module without ever calling the import method. Conversely, it's very easy for the import method to get called multiple times.
Very little advantage in this case. It just so happens that in the same loop I'm also playing around with @ISA and past experience has taught me to alter @ISA as early as possible. Modern versions of Perl are pretty smart when it comes to invalidating method resolution caches, but force of habit makes me put any @ISA alteration in a BEGIN block unless there's a good reason not to.