Not too familiar with that process, but as far as I understand, these routes (i.e. correspondent banks per currency/country and their reachability over settlement networks) are called "Standing Settlement Instructions". SWIFT does seem to offer these as a service [1].
But just like the messaging layer, this can be done via other means. For example, here [2] is Citibank Poland declaring their reachability for various currency transfers.
As for the messaging service itself, I believe that cutting off SWIFT SSI access would help in disrupting payment flows in the short term, but in the long term, sanction lists are the real enforcement mechanism.
As others in this thread have already said, these are a very powerful indirect stick when implemented as "you must adhere to our embargo lists, or we will prohibit all of the banks in our jurisdiction to do any kind of business with you, whether for embargoed clients or others".
