Another option is to just have a warning about excessive science spending but that might be more annoying than convenient.
TBH, I don't think it's necessary/desirable for your patch to auto-adjust the slider-setting itself.
But a(nother) simple end-of-turn pop-up reminder on the last turn of research ("Research will overrun by XX beakers this turn. Do you want to reduce Science spending?") — with a link from the pop-up directly to the Domestic Advisor, if the player clicks "Yes" — would probably be enough. I don't think this would be annoying, since it's only going to show up every 4T, at its most frequent.
Or if the problem is the player forgetting to crank Science back up over the interturn (using "WTBP?") or before the end of the following turn, then a pop-up could rather warn about a low Science-slider setting instead? The drawback to the latter is that it would also show any time the player was
deliberately running low SCI% — but there are generally 2 circumstances when that would be done:
(1) when treasury is low (gold < 50?), and/or a higher SCI%-setting would send the player into the red
(2) when a tech can't be researched any faster than [max. turns-to-research value] at [max. SCI% cap], so it's preferable to just bank gold
So maybe at least those 2 conditions could be set as excluders for such a pop-up?
Alternatively, a "Low SCI%" pop-up might only be show if the 'Beaker-overrun' pop-up had been shown on the previous turn (so that would have to be recorded somehow), and/or — probably the simplest/best option — if the "currently collected beakers" value for the new research project = 0.