Anytime an IP is excluded manually through your ClickCease dashboard, it is blocked permanently (or at least until it is removed from the manually excluded IPs list).
It also takes precedence over any IPs that have been excluded automatically.
Google allows to block up to 500 IP addresses or IP ranges.
For the sake of simplicity, say you manually blocked 100 slots of available space.
That means that system will only have 400 slots to rotate IPs in and out of your exclusion lists.
For more information about what happens when this cap is reached see here