I have done this swap from an SWM5 to a SWM3 and back again a few times with my new camping setup. Initial alignment was done with a SWM5 and when I did the swap to the SWM3 I noticed a slight drop off in signal levels. I also re-aligned the dish with a SWM3 initially and then swapped in the SWM 5 and actually got better signal levels with no further alignment. So for me, I don't anticipate having to re-align in the future when doing the swap. YMMV.
The only thing I had to ensure I did was to go into each connected receiver/dvr and rerun setup. When doing so, my receivers automatically detected the change and adjusted their settings accordingly.