a waterline is a waterline....those that differentiate between a saltwater line and a freshwater line are cutting hairs that dont need to be cut.
a boot stripe and a waterline are two different things... a boot stripe is a decoration, whereas a waterline is a telltale marking.
once you know your boat, you will be able to look at it and tell if its balanced the way you want it.
many people have had the water line raised because of the loads they are carrying, and others like the look of a thin waterline, even though they have very little in the boat.
you can either raise or lower the waterline as it already is on the boat, which is probably the same line as the boat design called for originally...
if you sand down you will find the original lines under the layers of paint...
or, you can sail the boat, readjust the loading, and the rigging, then sail some more.... and fine tune it all until you get the boat loaded the way you want it for the way it sails and handles the best... then mark a new waterline about an inch to an inch and a half above the actual water level on the hull.... and have it all changed to those marks.
and add a boot stripe to it if you like...