ChaoticKinesisit's very minor, and usually very expensive. it has to do with the metal used in the cable; if I remember correctly, some IEMs get marginally brighter with silver cables (higher silver content would lead to a slightly brighter sound) and copper for the lower frequencies (this one i'm not very sure of). either way, unless you're sitting on a pile of money its just not worth it. not to mention that the connectors on Shures wear out the more times you unplug the cable (they wear out too soon from personal experience) therefore it makes these kinds of upgrades even less worth while as it may compromise your IEMs on the long run. The general rule for MMCX connectors is dont unplug it unless you have to.
You're honestly better off spending that money on a nice portable AMP and DAC or a DAP, and taming the sound to your liking with software EQ. or as i'd suggest, just make sure its a sound you'll enjoy, rather than purchasing for the hell of doing so.