all that is needed is a barrel change and new mags?

The ejector on a 9 is usually too long to allow ejection of a loaded .38 Super cartridge.  It could conceivably cause problems even with fired cases.

The extractor might need tweaking, but maybe not.

If you load .38 Super on the hot side, you might want to upgrade your recoil spring a pound or 2.  Probably not necessary with regular level loads.

Other than that, provided your barrel bushing is compatible with your new barrel, you should be good to go.

My 9mm SA Target shoots both well,no other changes but barrel and mag, although some 9mm 1911 mags will fit 38super cartridge just fine