Welcome John. It shouldn't be a problem if the router still locks firmly in the cylinder. Be aware that some of those routers with an adjustment ring really weren't designed to used upside down as the adjust ring held the router up at the desired position and the ring didn't necessarily lock to the router base so that if you turned it upside down it would fall out when unlocked. I found out that rack and pinion style adjusters will do the same thing. Luckily nothing broke when I learned that lesson.
Which router model is it? Someone here might have a dead one that is still in good shape.
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.