If you wish to soften the peel, soak the lemons in lukewarm water for 3 days, changing the water daily.
Quarter the lemons from the top to within 1/2" of the bottom, sprinkle salt on the exposed flesh, then reshape the fruit.
Place 1 tb. salt on the bottom of a sterilized one-pint mason jar. Pack in the lemons and push them down, adding more salt, and the optional spices, between layers. Press the lemons down to release their juices and to make room for the remaining lemons. (If the juice released from the squashed fruit does not cover them, add freshly squeezed lemon juice - not chemically produced lemon juice and not water.*) Leave some air space before sealing the jar.
Let the lemons ripen in a warm place, shaking the jar each day to distribute the salt and juice. Let ripen for 30 days.
To use, rinse the lemons, as needed, under running water, removing and discarding the pulp, if desired - and there is no need to refrigerate after opening. Preserved lemons will keep up to a year, and the pickling juice can be used two or three times over the course of a year.