Let's get them all in one place.
A) Should I power the amp off if I switch from bold to spongy on the power section?
B) As above, do I need to power it down if I go from Diode to Recto Tracking?
A) The bold/spongy is part of the power switch, so you don't have a choice but to power it off. Just make sure to first put the amp on standby, wait a few seconds (it takes a bit to discharge the output section), turn it off, wait a few seconds (just in case), and then turn it back on in the new setting.