If you really want to tighten up the slide it can be done.
Johnny Glock videos for just such an adjustment.
It is semi brutal with a hammer and if you've not done this before or don't have spare slides don't do it.
I suggested doing this sometime back and got slammed for it and the post was shut down.
A loose slide, especially one that is loose up and down, will change the relationship between the crucifix sear and the striker. As the slide rises, the sear slides down the striker. Johnny Glock states that Glock itself allows 1/3 of the sear to show below the striker and the gun is still safe. He makes his guns so that100% of the striker makes sear contact for safety reasons.
If the slide is pushed up as far as it will go and that usually happens if a loaded mag is put in and the sear does not show below the striker, you are safe and according to Glock, you can have 1/3 of it show and still be good.
I tightened up my G19 slide as he showed it with a slightly modified method other than just smacking the slide with a hammer. I have done it to 1911's and both the Glock and the 1911's were successful. It is not of the faint of heart and because Glock slides are quite hardened, they do have a chance of cracking. My sear makes 100% contact with the striker and the slide has no movement.