By "buffer" I mean add something (like lime) to help neutralize the acidity
... not too much or it'll end up too alkaline. I also don't really know if
you need to do that or not ... my experience is limited to buying packaged
seed starter mix and seeing 'peat moss' listed as an ingredient. (By seed
starter I meant to grow your own vegetables or flowers from seed in little
trays or pots, not for grass!.)

One year ago, I did a soil test on my yard, and the result is fine. I
have a feeling that spreading out the peat moss over my lawn will not
change the acidity because the lawn space is very large relative to
the three bags of peat moss.

This sounds like a plan to me.

Jay Chan