Your existing data wont be effected after you enter you enter you licensee key and reboot. Once all license keys are entered to support your storage capacity then you data will be available. There is no reboot for the activation.
When updating from b4786 to b5626 there are mostly driver updates but if you are doing any iSCSI Auto Failover then make sure to that you have the Aux enable for each VIP. You can read the release from your User Portal.