Yzer, I wanted to be sure you're aware that the ribbon cable on those older generation screens are especially sensitive to any jostling, movement, or folding. I think it's due to the fact that the cable is thinner with more of it exposed and "in the wind" so to speak. The 1st gen V3 parts that I used as examples during my YouTube video are the result of that little lesson.
After the first time I took my 1st gen V3 apart and put it back together (Jun 2013?), the screen would occasionally display artifacts across the top or bottom row of pixels on the screen. I wasn't what you'd call "excessively rough" around that ribbon cable that I can remember, but I must have done something to it. The last time I dismantled it for the newest Omron switch (2 months ago?), I attempted to re-seat the ribbon cable. I thought it might have been pulled out a little since the ribbon cable looked OK. I was very conscious of the risk that I might make the V3 unusable, but I was willing to take the chance. At the time, I had my other V3 (2nd gen) and my new V5, so I wasn't going to be without a backup. I'll admit that those screen artifacts were really bugging the heck out of me, and that probably pushed me more than anything else to take the risk. With the card out on the bench and being powered by an 18650 battery holder, I could get the screen to come back up for a second, but fiddling around with the ribbon cable only seemed to make it worse until it finally said "enough, I'm done".
At any rate, I'm not trying to dissuade you from changing out the button (on the contrary I think you should definitely do it). Armed with the above, I'm certain it will go without a hitch for you. I did a few of these 1st gen mods after that first bit of bad luck on mine, and none of them had any problems afterwards.
Edit: The button I used in the video came out of my 1st gen V3 since I installed it and ended up removing it the same day.