Wouldn't they still work?
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good source of everything to do with RM frequencies
http://www.gbaudio.co.uk/radio.htm
The old frequencies would still work but may be prone to interference from other equipment using the old frequencies. Also they may simply be illegal!
As regards the override when speaking, I don't know of a mic that does that, its usually a facility on the mixer (as per my Citronic 10:4)
There is a mic override button and two knobs that allows the bite point and amound of reduction to be controlled.
Don't like it though, I'd rather control it myself, though I know that would be difficult from 60ft away!