Question:  Our theater is currently using the Clear-com PS 452 unit as our main intercom unit and because of age I think it is time to replace it. What new unit does Clear-com currently have where I can simply unplug the old one and plug in the new without any major rewiring?

Answer:  The PS-452 two channel party-line power supply was replaced by the PS-232 and later on by the PS-702 Encore party-line two channel power supply. 
The PS-452 was a 2RU rack mount unit with (3) 3-pin male and female XLRs for channel A and same for channel B.  The later version PS-232 and PS-702 are 1RU rack mount units that are only equipped with (3) 3-pin male XLRs per channel. 
The PS-452 could supply 30Vdc at 800mA per channel, maximum current capacity was 2.0A

The PS-702 can be used to replace the PS-452 unit