Archeologists regularly are going off shore to see settlements a few thousand years old, in 30 feet of ocean water. What does this say about the warming trend going back a few thousand years pre industrialization?
That depends on the settlements. There are many Greek settlements far under water, but this has nothing to do with climate. It has everything to do with earthquakes. There is more that changes the world than climate.
Archaeologists also regularly go to mountains to see fishing villages that are thousands of feet above sea-level. What does that say about ocean level decreases back over a few thousand years pre-industrialisation?
In relation to areas that were once occupied and were just above sea-level, which are now below sea-level or well above it, what are the various known methods to achieve this?
Islands have risen out of the sea and other islands have sunk back into the sea even in the 20th century. Investigations at the time established that tectonic or volcanic activity was the likely source of this up-down movement.
Don't be so quick to jump to the conclusion that the sea level is rising to any significant degree..
One question that is completely ignored is where has the energy been coming from to melt the land-based ice to cause significant ocean level rises in the short periods envisaged. The quantity required is so huge that there would be other effects on the environment before any large scale ice melt would occur. These effects would have long wiped out all life on the planet first.