Curious; was this an RNAV and did it not give you a top fo descent because the FMC wasn't re-cruised? So long as you get the top of descent, or more specifically, so long as the VNAV is giving you a path, you should be good. For sim-ism, unless there's something funky going on, the only time you should need to re-cruise the FMC with an altitude is if you're not getting a top of descent, and thus a VNAV path. In that case, putting in your current or lower altitude (depending on where you are on the arrival or procedure) should be enough. All you're doing is telling the box and sim where you are, and it is more of a sim-sim; the box uses that to draw a line backward from the bottom of the approach to where you are, to create a top of descent. Protect altitudes with the MCP. With that, you are able to get a VNAV path and once you're on the path, the only thing you'll need to do thereafter with altitude setting changes is to insert the missed approach altitude once you're several hundred feet below that altitude (to prevent chasing it, leveling off).

You're absolutely right, though; go-arounds are free (unless you're out of fuel. Then they're expensive).

I'm curious how selecting the FAF altitude in the box caused a descent below that altitude prior to the FAF. Were you in VNAV Path, and then caused the FMC to recalculate, and lost Path? What was the FMA telling you?

Don't play "overachiever." If it's working, follow your procedure, don't change anything that doesn't need changing, or get creative. Remember the basic truth of all training: cooperate and graduate.