I got my iPhone X’s battery replaced by an authorized repair center. You can’t tell whether the phone has opened or not. They worked that cleanly (no, it’s my phone. The serial number is the same). It’s waterproof and has no witness marks telling about the repair.

Moreover, they changed my speaker for free, because it was defective or damaged. I didn’t know that. I only learned after getting my phone with service summary report.

I had mine done by Apple at an Apple Store and then got it wet two days later. It was destroyed instantly. They gave me a new phone at no cost.

As a result, I now recommend AppleCare replacement over any repair, if the water resistance is important to you.

I'd say it depends on brand of pre-cut adhesive seal you use.

But normally (and if done correctly) it is watertight and opens +- the same.