All or some clients will have to download a new catalog. Depending on how you implement, either by using one of the existing WSUS servers or standing up all new WSUS servers, your clients will need to download the entire catalog from its new WSUS source. You should plan to remove existing SUPs one at a time to slowly cutover clients. (Good news: TP 1604 will allow you to force clients to a new SUP via Client Notification. This will eventually allow you to cut over clients in a surgical manner vs shotgun style, once it reaches production builds
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