when you change the Units of a model, choose do not scale …if you scale it, the size of the object itself will change… for instance, a 5" x 10" rectangle will become a 5mm x 10mm rectangle if you scale… the object gets much smaller while the dimensions stay the same size which may lead to what i assume you mean by smothering…
whereas i believe you’d like to simply change the units without altering size? 5" x 10" rectangle stays that size but feedback is now in metric? 127mm x 254mm
if so, don’t scale when changing units