Hi Noah, welcome.
That planter looks quite full now, Noah. Were you planning to take out those existing plants? They look quite nice as is. Oleander can get quite large and would give you much litter on your patio to sweep up.
You didn't say how tall your existing block wall stands. If it's 6 feet, then a 2' lattice topper might help. Are you trying to block the view down into your space from your neighbor's balcony? I know I'd want that, too.
Since your planter is full and you have concerns about roots, perhaps vegetation isn't the answer. Maybe the answer lies somewhere between extending the block wall up to the 8' max height allowance or metal garden art (that plays off your existing pool fence) staked up, yet behind, the existing bushes? Depending on what you go with and your wind load, perhaps the stakes could be anchored to the block wall, thereby not disturbing the existing root system?
Finally, perhaps an arbor with a top that slants away from the balcony view? Your HOA may have regulations on fence height, but can they regulate an arbor height? Sometimes the most simple solution is the most effective. Would a large offset tilt patio umbrella do the trick?
Just some ideas, Noah.