This is not a constructive topic. Leave your upstream's router alone. To answer your question, yes, however its typical to filter connectivity directed TO the gateway IP.
Another method is to use a gateway IP on non-advertised IP space, which is less computationally expensive than ACL's at the edge of the network. However, it does result in missing hops for traceroutes through networks who use reverse path forwarding (e.g. Level3).
You could also alway just null route your gateway IP's, which will not affect any actual routing.
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