I know it requires board level soldering. I saw the first two videos of a three part series that seemed pretty good. But...

What generation watches are you having this issue on? Are you replacing the entire assembly or just the glass/digitizer? I've replaced a good number of screens on the first gen and Series 1 watches and so far I've found out a few things: 1. You can't replace just the digitizer unless you also have the service cable and can flash the firmware. I've heard you can replace just the digitizer and then run an update, but the timing on this makes it difficult and I've never tried it. 2. Some Apple Watches just don't like certain screens. I've seen this happen a lot when I have pulled assemblies from a parts donor and put them on the watch to be repaired. The donor assembly either won't display anything at all, will get stuck in a boot loop, get stuck in the flashing charging cable loop, or touch doesn't work. So far I've had pretty good luck with disconnecting and reconnecting the battery, swapping for a new battery (probably the same as a disconnect though), and running an update with the new screen in place....

There's no way to guarantee that it would still have the same water resistant rating. Also, the replacement adhesive strips I have found so far are a bit thicker than the OEM one. So after you re-set the screen in place, it sticks up a teeny, tiny bit higher than it did originally. Literally, we're talking a fraction of a millimeter, but it is enough to feel. And if you really look closely, you can see the difference too. Does that matter? Maybe, maybe not, but personally, I worry a little bit about the edges of the screens being that much easier to chip. Personally, before I did anything else, I would try picking up a good screen protector (probably one of the plastic ones like the stuff from Armorsuit, not a tempered glass one) and see if that covers up the scratch enough to not bother you so much.

**Editing to say that I am 100% sure you can swap batteries between the First Gen and Series 1 Apple watches because I’ve successfully done it countless times.** I'm pretty confident that you can use a battery from a Series 1 Watch in an Original Apple Watch. The internals between the Original and the newer Series 1 are almost identical. (The processor was about the only change.) In fact, if you order a replacement battery from ifixit.com, the batteries are listed as being compatible with either Watch. Also, the details about the used OEM batteries listing even says that they are taken from either an Original or a Series 1 Watch. Apple Watch (38 mm, Original & Series 1) Battery Apple Watch (38 mm, Original & Series 1) OEM Battery Series 2 is different though and cannot be used in the earlier models.

Etechparts has precut replacement adhesive that are the closest I have found to the original Apple stuff. Most places I have ordered from use a black adhesive that is thicker than the original.

Etechparts uses a clear adhesive and after replacing the strips below and on top of the Force Touch gasket, the watch went back together perfectly. It didn’t have the slightly raised lip that even one layer of the black stuff seems to cause. (FWIW, I always leave a couple heavy books on top of the watch overnight to help the adhesive set.)