For an amateur radio repeater use tag communication:amateur_radio:shift=* to assign the repeater receive frequency offset from value of key communication:amateur_radio:repeater:frequency_out=*.
The shift value is given in (Hz). It has to be algebraically added to the "frequency_out" value to find the repeater's incoming frequency. This value could be negative.
Typical values are -600000 for 2m repeaters, or -7600000 for 70cm repeaters.