Bit of a silly topic perhaps, but curious if I am missing anything:

Assuming the sail has correct downhaul tension, are there are any changes/consequences to be expected when the entire rig is, say, 4cm higher than it would be if it were pulley-to-pulley at the bottom?

For a simplistic example, if the downhaul number is 374, you can rig a 370 with 4cm extension and pull all the way down to the bottom pulley. Or if you had 8cm extension, you can downhaul until you are 4cm from the pulley. The sail has the same tension/shape in either case. Your body is now 4cm lower at any given point on the sail, which should be mostly irrelevant unless you got silly with the number.

Is there anything else that will happen doing this vs. rigging with the minimal base extension? There are a few different reasons for doing this, one of them is that on some very tiny sails the boom cutout is too low. Raising the whole rig allows me to have the correct boom height. I've done it countless times with one particular sail and its seems no different to me.