Why don't use the catalog configuration? I mean, as part of the service specification configuration in the catalog, you can set default values for its characteristics, or feature characteristics. You can also manage versions of these specifications, so if the default configuration changes, you just need to generate a new version of your specification with the new values. The SOM component responsible to execute the reset operation would only need to get the last version of the specification and apply the default values.
In that case, if you can't store this configuration in the catalog, and you don't have a way to recover a valid previous configuration from the inventory, the only way I can think is to implement logic in SOM to recover the information that you need from the legacy systems.
My point now is which is the right place for that? I guess that you have a SOM component, which has orchestration and decomposition capabilities and provides the TMF641. I guess that it is also able to make calls to the TMF640. If these suppositions are right:
Well, this is just another option; perhaps more 'standard'. Hope it helps.