Old Server to new system, no access to old server

Funny situation.

There's an old server at one of our locations that nobody has access to root on, so nobody can get in to change IP addresses.

We're migrating remaining devices off of the old network and moving them to new...but this one. This one is a problem. Its still a mission critical device locally until the new replacement is installed, which could be months down the road.

I'm wondering if it is at all possible to cheat our way out of this without having an IP conflict, as the network (old system) that it is on also exists on the new system--elsewhere.

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So for argument sake I'll say that this machine has an ip of 10.10.10.156/24

10.10.10.0/24 is a network that is tied in to OSPF elsewhere, and though there is no potential IP conflict (at that particular IP), this still poses a problem.

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I am resigned to leaving this and the ridiculous switch setup in place for the time being for the sake of leaving this thing online until the service itself is replaced by a new one.

I'd much rather have access to an old password book, but looking for other options.

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