How to setup LOV of reasons for updating Repair Order Types

A new functionality introduced in R12 seems to be the possibility of updating the Repair Type that a repair order was created with. This seems to work well and easy to setup. We can specify from which RO type to which others RO types you want to enable the changes and for what RO statuses you will allow those changes.

However, there is nowhere I can find information about how to setup the reasons (they are defined in a standard List of Values of the Repair Type Update form, but only one default value is enabled).

We want other values than the standard "Unable to Repair" to be available as reasons for changing the repair types. Which is the name of the standard lookup or list of values where I could define new ones? Anybody knows?