Any IP address can be used to register a masternode

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If one uses a (random / not "owned") IP address when registering a new masternode, that IP address cannot be used by its legitimate / current "owner" in the PAC Global network, in worst case, for indefinite time.
In most cases, where standard VPSs are used, this is not relevant, since one can always have another IP assigned to it or get a new VPS.
This is relevant for all who use fixed IP (ranges of) addresses assigned to them, like larger shared/full masternode providers or individuals acquiring or having fixed IP address(es) assigned to them by their providers.