It is possible to programmatically adjust the brightness of the Sparkles using a potentiometer.
I have included an image with two examples of code on. The top section of code will allow you to adjust the brightness of white, whereas the bottom section shows you how to adjust the brightness with a particular ‘shade’ of colour (e.g. purple). The wait statement helps to eliminate any flicker, but it may not be necessary in your case.
I hope this helps, and if you have any more questions, feel free to ask.