No amount of brain training will change your genetics. ADHD has a significant genetic basis (thinks like the DRD4 allele differences discovered by Robert Moyzsis), so those things won’t change.
However, diet, exercise & meditation will help anyone, ADHD or not.
When it comes to medication, I wouldn’t worry about moderate doses of Methylphenidate messing up your brain. High doses (i.e. 80+mg) haven’t been well studied over long periods, and the drug has a plateau effect, so I’d avoid the high doses.
Instead of lumosity, I’d recommend the free site http://cognitivefun.net/
I used it for a few months, logging my scores in a spreadsheet to try to measure the effect of medication. 40mg MPH (2x 20mg Ritalin SR) made a small but statistically significant (~5%) improvement in my PASAT.