Strongarm

The biggest problem is likely complex variables in the variable table (nested arrays which become serialized). Here is a solution for changing only part of a complex variable: http://groups.drupal.org/node/52588#comment-144213 (if this doesn't work or is awkward, i have a similar solution that i can dig up, but i believe mine is less robust).

I think drupal_array_merge_deep() may be the function we want to use in these cases.

Strongarm does not have its own administration page (that does anything). Add variables to your export by going to the Features administration page.

Background

http://developmentseed.org/blog/2009/dec/04/strongarm-2-leaner-and-meaner