Some people also switch out the extractor to make sure it pulls out the empty 9mm shell cases. If you do this, which isn't necessary, but may increase dependability, you switch the extractor (to a Lone Wolf LCI 9mm model, which has a marking making it easier to identify $7) and a spring-loaded bearing (Glock OEM is fine, also from Lone Wolf $3). You can keep the spring in there and the plunger, since those are the same for 9mm/40/357.
These changes take a few minutes to convert and are not necessary. But if you plan to keep it a 9mm for longer periods of time and not just a range session, you may want to do this for only $10 and 10 minutes.
.45acp, .40 S&W, 9mm, .38 Spl, .380 acp, 22lr
12 gauge, .223/5.56x45mm, 30-30 Winchester
2 Chron. 7:14 Christians must seek His face