Why would you go from static back to dynamic? What might be the use case?
And why do you think, that dynamic would not be like its name: dynamic?
If you want the device to always be available via the same IPv4(/IPv6) address, then make it static; if you do not want this device to be a server, then don't make it static.
If you (e.g. by error) made a dynamic lease static, the lease can be deleted, then (before the old lease ends, as the client does not know about the server changing its configuration!) the client will first try to get that old IP address back, and if the DHCP server does not see it free, then it gives the client another address, otherwise, the client gets back the old address (but this time, it will be dynamic).