The one way you might safely get away with this - assuming the antenna is a multibander - is to use bandpass filters at the antenna connector of each transceiver, with a band-stop filter at each port of the switch assembly. The stop filters are tuned to the "opposite" frequency range, much like a set of duplexers in a repeater system.

If you substitute a power combiner and pass/stop filters, you could eliminate the switch altogether and use both radios at the same time...assuming different operating ranges for each.