This might be a liquidsky question.
I've had a bunch of orgasms with sounds or solid plugs inserted. The orgasms feel good and normal, except no semen comes out. When I pull out the sound or plug, semen flows out like a slow stream of urine. I've waited several minutes to pull my sound or plug after orgasm, and this still happens. It's kind of weird.
Maybe some of my semen goes into my bladder, (retrograde ejaculation), but not all of it. I would guess that longer sounds or plugs would cause more retrograde ejaculation if it does happen. I'm not sure what a Guyon sound does to semen flow when its inserted through the prostate and into the bladder during an orgasm. I'll have t try that.
See https://en.wikipedia.org/wiki/Retrograde_ejaculation for details on retrograde ejaculation.
The article says some primitive tribes use squeezing or pinching the urethra to block ejaculation as a means of birth control. If it had ill effects (other than not working as birth control) or it permanently blocked normal ejaculation, I doubt these tribes would continue the practice. The only injury risk cited in the article is possible penis numbness caused by excessive pressure on the pudendel nerve. It sounds to me like this risk is only due to pinching the urethra and hitting the nerve, not plugging the urethra from inside.
My penis hasn't gone numb or permanently stopped ejaculating in the normal direction. I wouldn't worry about it.
Could having orgasms while sounding actually be good for you? Some alternative medicine practitioners and eastern religions claim retrograde ejaculation is a way of conserving life force energy. Check out the end of the article. I'm going to have to insert a long sound and have an orgasm every day for a month to see if I feel better.