I have a 2015 SX240 and had a new Bimini top made over winter.this year, Made locally from the original, but had 3 .0" added to the center. Wanted the front to come down farther. To do this I had to purchase new tubing and ends.
So, to address your question, here is an option, may not be the best, but tossing it out there. If you cannot do it at home, take your bracket and have two more identical holes added with chamfers in between the existing holes.
Once this is completed, fill up the inner part of you railing with either an epoxy, or silicone, kind you use for bathrooms (Clear),( Just fill area under holes.)
After it dries, using the two existing screws. Place the clamp back in place and screw into original holes. The silicone with keep these screws semi secure from rattling.
Then using two new holes in bracket as a guide, center into the hole and drill and tap 2 new holes, if these are self tapping screws then will just need to drill. Will need to find similar screws.
Once this done. Place your original poles on the top section of the Bimini and and pull snug, but not too crazy tight, measure how much longer the poles need to be to satisfy what you think is reasonable.
Go to Sailrite web site. At top is menus, Click Hardware, then Tubing, find 7/8" and you can either buy (2) 2 Ft pieces ($11.90 Ea.) or (1) 4 Ft piece. ($23.80) Length of each side is about 21.5 " I think. Will need to cut tubing to correct length . I bought a Rigid tube cutter "For Stainless Steel" about $35.00 but does a perfect job
Then go to hardware, Eye ends, and get (4) 7/8 eye ends. ($6.95) ea. The eye ends on the factory ones are riveted, so no reusing them. (at least mine were)
One thing to check, on my original front poles there are two setting for length. There is a push button that you can push in on the side of the poles and pull the tube longer or shorter. 2.0" difference in length, make sure, if yours are adjustable, that they are on the longer length, will never get to the shorter length without bowing the poles, or stripping out bolts?
If you cannot find the correct screws at a hardware store. The factory Yamaha part # is 90167-08S10-00 need 2 $2.95 Ea. Local dealer or order form yamaha parts on line.
Trying to weld on anodized aluminum will ruin the look and always possible to get burn spots on interior?