Maybe you could get another bucket, pull the plant (screen and all) and set it on the extra bucket while you do your changes.
Yes, I do this all the time with the Binky Buckets. My plants are not that big at this stage and no screen to deal with but I believe this would work just fine, not the easiest but works for sure. I've read where those site tubes are not the greatest thing, holding stagnant water and not the best thing.
Have you thought about installing a bulkhead near the bottom of the bucket to use for a drain line? A ball valve to turn on/off and a length of tubing to reach your drain line, may need a pump in your situation.
Now I’m interested at what strength ml/gal you are dosing the GH Trio. I just made a gallon to top off my res. I did 50% of the light feeding schedule. Keep in mind that my water out of the tap is 100ppm. I added powerSi, calimagic, the trio, fulvic and PH down to go from 6.3 to 5.8. The ending EC was 1 and the PPMs were 540. Now trying to stay close to SLGs recommended 400PPMs, I added plain water until I got down to .9ec and 440ppm. I would prefer to not add the plain water at the end if possible. How are you guys dosing the trio? Sorry Moe, I didnt understand your previous post on this.
I do not think there is anything wrong with adding plain water to dilute your nutrient solution, I do it all the time but I have to remember to add a bit of cal/mag except for late in flower when I do this.
Using my Binky Buckets for the example I know, I just pick a feeding ratio off the chart, either light or medium......ratios are going to be the same regardless. So when I am building the res in the BB, I make a large cup full of concentrated nutrient water at the ratios on one of those charts, then I add this to the plain water in the bucket until I get to my target ppm.
When I get to my larger systems, I record my starting ppm and ph, then I add what I call "One Round" of nutrients to the res and see where that lands on the ppm. Then, assuming I know my target, say for example 400 ppm. Lets say one round brings my ppm up by 50 ppm, started with 100. That gives me 150 ppm. Then I do the math and figure how many more rounds I need to get to my target. I always come in lean, then add a bit more if needed. Sometimes I deliberately under fill the res, load the nutes and leave that room in the event I need to dilute things down.
Hope this makes sense, not a lot of time atm.