You can pull good clones until they are in bloom. Flowered clones can be flipped back, but it adds a month of plant confusion that is best spent with new plants.
75 days is fine as long as the nutrient uptake is consistent.
If it is still growing, you can keep it going.
No joke, and don't get your hopes up, but depending on your setup(600W+) you may be in danger of breaking branches with the weights of the buds! Stakes and cord are all good! Protect your girls!