I have done this many times. I used to own a production machining business. What you want to do depends highly on if the existing product has patents and if so, are your changes significant enough to not infringe on said patents.

It isnt cheap, but the pay off is nice if you know how to market the new design

Its weird. I personally have a guy and im a guy. My guy is a kinesiology focused professional, helps with after race correction.

Adding to this, my ex wife has been independent for close to 15 years. Men are successful in massage therapy in the south in 2 catagories honestly, seniors and sports therapy. She turns most all of her sports related business to a male friend of here. They share referrals for seniors as well.