I hear you living by the sea with a 4 month summer. I'll leave the rulings to rules specialists.
More grip has some options. Different discs and plastics with lower weights (not great for winds unless it's a wind beater and you don't drop the weight too much), individually zip loced towels way more than you had, grip enhancers bees wax, pine tar based stuff Gorilla grip what have you. Perhaps even a birdie bag. Rain clothing and an umbrella to protect the bag, disc and towels plus the hands. The skin can dry up and get slick with water and coldness so you might want to experiment with skin moisturizers. Perhaps some glove with grip pads works i haven't found a perfect one despite looking. Sand paper does not last and i've not found any kind of tape that works except perhaps anti slipping tape but they tend to be coarse so they can abrade the disc away and primo plastics tend to be carcinogenic in powder. So rain might help there. So far i haven't tried out the anti slippage tape i bought but it is too coarse. I wanna test the idea. I'm afraid of the glue being designed for floors not skin being unhealthy so i think i'll test it with fabric sports tape in between the skin and the anti slipping tape. The fabric and plastic sports tapes i've tried fall of with use in the rain. Perhaps sports tape supported by plastic based anti slipping tape might be just the ticket. Or gloves covered with anti slipping tape. Again rules experts are needed to say for sure which options are competition legal.
Discing up powering down reduces gripping power needs because you throw as far with reduced power. The trouble is some discs fade out so generally speaking you need low fade discs in powering down. Like Pro Beast. For grip with less grip GL River is another usual suspect. A new kid on the block could be light Quasar. It ain't tacky but it is the tamest really long disc but it still is a power players disc so i can't recommend it yet. River is the best power wise if Leopard Star is too flippy. I wouldn't make that determination until you have good form.
Flat shots need running on the center line of the tee and planting each step on the center line. Anhyzer needs running from rear right to front left with the plant step hitting the ground to the left of the line you're running on. Hyzer is the mirror of that.