To echo what Steve said I did the same to align them. Parked the car in front of a flat surface with the headlights installed and no lenses and did some tweaking. I went with a full kit so it had adapter plates that go into the headlight housing which resulted in very minimal tweaking.
This was without any tweaking after installing the driver's side:
Steve is more experienced so I'd listen to him if he has a different recommendation but I just used a healthy amount of Loctite to around the nut and threads. I have a pretty stiff suspension and there's crappy roads where I live so my car gets bounced around but they have stayed tight FWIW.
Regarding resealing my issue was that my passenger headlight was the first to be baked in the oven to loosen the sealant and because I was nervous about melting the headlight I kept removing the headlight and trying to separate the lens from the housing over and over so the sealant was getting pulled around a lot and in the end when I resealed that headlight it was unevenly distributed and I didn't get a good seal on one part. Driver side I waited and wasn't impatient and it resealed perfectly.