Thank you both for the feedback, that does clarify exactly what I was looking for. I'm also realising that I had not correctly grepped the operation manual, as the exact answer to the question is on page 4, second paragraph:
" When the system is placed into the Run mode, it will sequence through all enabled mode configurations in turn. This allows you to program sequences of bands, if you have connected the optional relay-switched Low Pass Filter (LPF) kit. "
Still, I'm glad I asked the question, as I now have some more interesting things to consider.
Andrew - thank you for the pointer for the thermals cycling reminder during CAL, and you've given me some useful pointers overall and I'm letting the ideas sit while the old subconscious figures it out. I have possible solutions to hand but it'll be the making elegant of the solutions that will be the fun bit. I can see a possible external routing of a control cable along with two short coax cables in one possible solution, or putting some fans in. The kit as a whole will hopefully be sitting in a moderately sized weatherproof box along with a solar charge controller and voltage regulators for 5v 7.5v and 14v for the kit and selectable PA drive voltage. More experimentation to be done after kit arrival/construction and then actual testing later in the summer when I'll be allowed to transmit..
Ken - perfectly clear, and sense has been made. I think I have a good handle on the relay kit implementation and operation, it is a nice setup. Regarding the ATU performance, I have en route to me at the moment Ebay/Aliexpress self-solder kits for the ATU-100 designed by N7DDC, and I also have the LDG Z11 Pro 2 ATU with a listed minimum of 100mW transmission to tune which (if performing to spec) will work just fine for the intended purpose.
Again thank you.