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I raised mine because mine is a saltwater fishing boat. If lowering, your issues will come with the rail "posts" that are angled. Without seeing exactly what you have and any discoloration or scratches where your "tees/wyes" were originally (because as you lower the whole bow rail wants to slide backward). Your rear mounts stay fixed and an extension goes on the front. It may make the old top rail hard to re-use. Kinda a shot in the dark for true recommendations. I personally would try to keep the boat mounts as is. As you need an extra length do your cuts at the center of the rail fittings. You will need some rail on hand. If my boat....I would lower the set up using the old hardware and design around what makes sense before any cutting. The rail is bendable by hand for soft sweeps. Do so on a big block of wood, go slow using your foot and arms, and keep holding it up to the section you are working at. Once set up use a perma marker (keep several colors available as you will be changing the lay outs ever so slightly). Make sure everything fits before "hotdogging" and scribe a line on the top for the match. I had to file/die grind the interior of the 1" rail for the 7/8" to fit. I found it was better for me to cut the pipe with a cutting blade on my 4" angle grinder than pipe cutter. The pipe cutter kinda pinched the pipe too tight to fit the hot dog. You are going to "persuade" the 7/8" pipe into the 1" so you better be pretty accurate to start. As you bend the pipe it stretches/oblongs so be prepared. Very very tight but no allen screw fittings.....I got a bag of self tapping screws (there is a vendor on this website that has them) and used the fitting's holes as a guide for drilling. If you have the allen screw fittings I would drill out the thread and go with the self tapping screw. Good luck, having it the way you desire is worth the work.
Garris

edit: I reflected a hair and I would guess the mounting furthest away from the bow probably the toughest to duplicate at home. I would tackle the project from that position as my starting point.