Does changing cable on iems gets better sound?

So can the cable make the change?

Nope. See:

In a blind test, audiophiles couldn't tell the difference between audio signals sent through copper wire, a banana, or wet mud

https://lemmy.world/post/43133553

$4000 Audio Cable vs $7

https://www.youtube.com/watch?v=QjvgL9_zL80

That being said, IEMs and headphones often suffer from bad cable contacts or near-broken lines, so simply replacing a busted cable with something not-broken could dramatically improve your IEMs.

It'll only make a difference if the cable is damaged or faulty to begin with.

IMO just get some cables that are comfortable.

So my Sonus 7hz cable is cutting sound when I pull it, which means I need new iems anytime soon.

It might very well be a break in the cable --- I've definitely had that happen to cables, especially when I repeatedly run over them with my chair's casters --- but I'd check to see that you don't actually get the same problem with another cable. I've also seen the audio jack in devices have the solder pull free before and need to resolder them (yanking on the cable does put some stress on the jack, and you don't know how it's attached to the rest of the device).