Change referenced index for a Foreign Key
Well, after continue searching I found this article


  Unlike a normal query, it won't pick up a new index due to statistics being updated, a new index being created, or even a server being rebooted. The only way I'm aware of to have a FK bind to a different index is to drop and recreate the FK, letting it automatically select the index with no options to control it manually.


Whereupon, unless someone can say otherwise, I will have to look for a time window to perform this task.

Thanks