I have been successful with getting a repeater down into the 440 MHz amateur band, and just got it installed a few days ago.
These repeaters are nice in that they are self-contained and have most of the functions you need on 440 MHz amateur repeater, and will accept external controllers. I started with 2 I picked up cheap at a Hamfest (the original RRX-450 is wideband only, so it is fine for Amateur use. The current RRX-452 is narrowband. Many of the RRX-450s were surplus when public safety/commercial users were forced narrowband.)
Issues:
1) The transmitters seem to go into the 440 MHz band without too much difficulty. Note that you need to activate the PTT via a local mic to tune the VCO to 4V, and it is the one changing of the 3 voltages when you diddle you need to worry about.
2) The receiver VCOs are more touchy - I was able to get 1 of 2 I had into the 440 MHz band. The other simply would not ever lock up, in fact, I could not get the VCO to lock much below 460 MHz. Not certain if there was a build where there were separate receivers for different UHF sub-bands. I did have the advantage that the input frequency for the repeater I was building was in the 449 MHz range, so not too far out of the manufacturer's specs. There are no frequency-dependent parts I could find on the schematic, but I suspect an RF engineer could identify parts that might aid in tuning outside the specified band.
3) For the receiver where the VCO did lock, I could never quite get the VCO all the way to 4V, it seems to work just fine at about 3V.
4) The built-in duplexer (4-cavity notch type) was not designed to go below 450 MHz. With longer screws (I replaced the provided 1" screws with 1.25" screws), I could get an adequate notch (about 70 dB) on the 449 MHz receive side, but not enough notch on the 444 MHz transmit side to be effective (could only get about 45 dB). I ended up just removing the internal duplexer, building a set of cables, and using an external set of pre-owned commercial cans, which works great.
5) The nominal output power of the RRX-450 is 8 Watts (Ritron's market is low-power single-site systems for malls, golf courses, and industrial sites). While this might fall short for system intended to cover a large metropolitan area, it is enough for a small to medium sized town, or even farther if you have an elevated site. If most users are on portables, this should be fine. Keep in mind that 8 Watts into a 9 dB gain antenna means you have an ERP of 64 Watts, which is respectable. Recall, however, that such a gain antenna may have coverage holes "under" the pattern of the antenna.
6) One of the repeaters came with a 30 Watt amplifier. At least on 444 MHz this proved very difficult to keep properly tuned and after a few days would drift off its ideal tuning and become a current hog, source of broadband noise, and not reliably increase the on-frequency transmit power. Taking the amplifier out of the repeater resulted in significantly better performance on both transmit and receive and far less power draw.
7) The built-in CW-IDer will not transmit the "/" required for the CW ID of amateur repeaters. This is especially frustrating, since the "/" is listed as an available character in the Ritron programming software; I contacted Ritron to ask and they confirmed that this is an error and the "/" is not supported. Thus, a simple ID-er or repeater controller would be needed to have a legal amateur repeater.
So, the overall answer is that the RRX-450 can be moved into the amateur band, but pick up a few if you can so you will have enough transmit and receive modules that you will have a few that will actually tune into the 440 band.