Is it safe to switch to generic mestinon® (pyridostigmine)?

Yes. It has been years since my patients have actually used brand name mestinon, (pyridostigmine) and the generic is likely quite comparable. Do not worry about this switch.
Yes. If you buy generic medications at a reputable pharmacy, in general they will be chemically the same as trade-name medications. This is not necessarily true at all for medications that are obtained online or from foreign suppliers. So be careful! read labels, and check with your physician if you have questions. Mestinon (pyridostigmine) can be critically important for patients with myasthenia gravis.