Plugin to modify Model/sku based on options

I have seen a lot of people asking for this in the forums, but haven't seen any clear answers.

Is there a plugin that will modify the model or sku numbers based on options selected?
You have product1 with a model of CA1234, you choose option A and the model becomes CA1234A or option B and it becomes CA1234B?

I use Openstock to add SKU's to options. Does the job very well if you have a smaller store.

http://www.opencart.com/index.php?route ... =openstock

Unsure if it will modify those options automatically but if you purchase your goods from your supplier the SKU should be different anyway.