Wouldn’t 7.62×45 require replacing the receiver, bolt, and mags on an AK?

Normally a cartridge change would require changing the bolt face, ejector rail possibly, mags maybe, and the barrel.
Realistically, not a feasible commercial change unless a particular round (that fits) suddenly becomes popular and widely available.

There’s no real reason to switch, unless the sales are there. And without a glut of ammo cheap, there’s no reason for anyone to change from the x39 cartridge. Some still wouldn’t.

Unlike the ‘modular’ AR platform, switching the AK barrel requires removing the barrel pin (no small task), then the barrel (you will need a press or other tooling). Assuming an assembled barrel, the barrel is replaced and headspaced then the pin replaced.
The ejector rails are spot welded in place.

Actually the x39 cartridge can be highly accurate, just not in an AK or with conventional ammo.
A friend had a PPC action Sako he had chambered/built for the x39 round, it was a prairie dog machine of the first order. Half inch groups at 100y were the norm assuming good ammo not mil-surp junk.
Properly handloaded the x39 AR’s are decently accurate also, again with good ammo not junk.

As an aside, a different friend has a Mini-30 that’s been rebarreled to .25x39mm, it’s a deer and antelope killer extraordinaire. But he’s stuck using high priced brass (PPC) that’s not ‘commonly’ available where he lives.

The Brits once tested the .280 British, very similar to the modern 6.8mmSPC and 6.5 Grendel, both of which have their fans and detractors.

In the case of the Czech round, it would require more than just simple changes, it would require redesigning the AK around the round, it being too long for the x39 magazine and associated mag well.
2.4″ vs 2.2″ roughly. Then we need to look at bolt travel distance, etc. There is more to certain engineering changes than many realize.

If one were wedded to the Czech cartridge, it would be easier to just start manufacturing the CZ rifles in the old cartridge and be well off.

Personally, I’m just going to stick with the AR and FAL platforms, the modular designs lend themselves to adaptability and reliability. Todays AR is not your grandfathers AR.