May propagate during growing season.....
disease resistance NOT aaffected by propagation & the yeald will be smaller since the branch(tip) will be out of production for several weeks & MAY be delayed so the fruit ripen late fall..... yes the bottom suckers may be used...

having a fall crop wont matter.most tomatoes dont set fruit above 90 degrees,anyway.when i grew acres of them,we would simply cut back the old growth abt july or when it went over 90 for a week,then continued to water and fertilize and had 2 crops from one planting.if you do cuttings,you'll have abt a 6 week delay on fruiting,same as if you cut back the old plant..cut to abt 2-3 ft from the ground.

That's a very interesting method, I've never heard of that. So once fruits stop setting due to high temperatures, they won't start setting again (when the temperature goes down) unless you cut them back? Do you think the extra foliage (shade) you get from growing tomatoes on a trellis will allow the fruit to set in high temperatures?

Actually I see that there are plenty of threads on this topic so I won't make you post it here. Thanks for the advice though, it showed me an important aspect of the tomato growing season that I did not know.