What “changes at the board?” Preamp changes will be heard in aux mixes, as will eq if aux mixes are receiving signals post eq. I have found Changes in effects to be disruptive, so I use a different reverb for IEM auxes, and no IEM mix gets any of the FOH effects.
The other options for avoiding all changes in IEM mixes are…
(1) use a separate mixer for IEMs and split signals before hitting the mixers (analog or digital splitters or tie lines)
(2) use two channels for every sound source that goes to IEMs on One mixer. One of channels only routed to FOH. (If your mixer has this flexibility, and you have enough inputs)