Hello santhumax, If you have all configured with your 16gb switch as your 8gb switch all should be fine.  As always make sure that all host & storage are failed over to other fabric and then fail back one at a time to ensure that connections are good and stable.  If you have any connections that fail, then you may need to reregister them.
Hi Support, we have 2 Data centers(DC1 and DC2) the ISL is connected between DC1(16G-SAN Switch) << to>> DC2 (8G-SAN Switch), now i want to replace 8G Switch with 16G. ON DC2 8G SAN Switch got another 2 Switches connected (via ISL). The same setup at Fabric A and Fabric B. i am planning to add 16G SAN Switch at Fabric B first, if i replace 8g with 16G will it effect other 2 SAN Switches connected?  may i know the best practice to do this? 
Replacing 8g Brocade SAN Switch with 16G which has ISL connection