The only thing I can possibly add to the above comments is that good transformer companies like Sowter in the UK will make a range of transformers suited to specific cartridge impedances. These are "loose" transformers that should be wired internally into the preamp which turns out to be the best way to add a transformer. No added contacts or interconnects and the transformer has additional shielding within the preamp. You just have to keep it away from AC devices like the power transformer. A good technician can make the addition 100% reversible.
Any electronic geniuses here?
When looking at a setup like this, LOMC to a step up transformer (SUT) to a MM phono stage, would changing the impedance of the MM input alter what the LOMC 'sees' at the input to the SUT? This is a purely technical question so please, no opinion pieces on the arrangement. Thanks