I’m following the instructions found at the following sites to configure Twitter Tools to use the Tr.im URL shortening service.
- How To Use Tr.im URL shortening with the WordPress Twitter Tools plugin
- TR.IM + WORDPRESS + TWITTER = GOOD
With luck <crossing my fingers, knocking on my head>, this will work.
Update. Success!
I'm Brent Logan and I've been here since 2004, writing about family, food, and fun. You can contact me at 
[...] it, you have to redo all the customizations, such as creating a functions.php filter to use Tr.im with Twitter Tools. [...]