A muscle that is inhibited does not contract. AKA, is relaxed. If you mean with ‘reverse Kegel’s’ just relaxing your BC and IC muscle, this is not dangerous, is just pointless. Having your BC and IC muscles relaxed just means a less firm erection and sperm coming out slowly. This. if you relax them whilst erect; but, as a form of exercises, does nothing. If you relax many time your bicep, this doesn’t become permanently weaker. Even if it was relaxed the whole day, just a few minutes of contraction would preserve its functionality, size, tone etc..
If you mean with reverse Kegel’s trying to piss without the need of it, it is dangerous and I’m not going to post any backup for it because, it is just a notorious fact. Really you never heard of anyone who forced himself to piss and blood came out instead than urine?
About the destrusor muscle, it’s me quoting wikipedia now:
“The detrusor urinae muscle, also detrusor muscle, muscularis propria of the urinary bladder and (less precise) muscularis propria, is smooth muscle found in the wall of the bladder. The detrusor muscle remains relaxed to allow the bladder to store urine, and contracts during urination to release urine.[1] Related are the urethral sphincter muscles which envelop the urethra to control the flow of urine when they contract.”
So, this kind of Reverse Kegeling is not about relaxing, but actually contracting a muscle. And this muscle does not inhibits the BC or IC. It contracts to perform another function. When you have an orgasm, a number of thing happens; actually the BC and IC muscle tend to contract and relax, and other muscles involved and chemicals released etc. etc.. So supposing that doing something that happens in a given, pretty complex context, leads to some unexplicable benefits, I am inclined to call it mysticism.