Bo Jackson had a hip replacement after damaging the ligamentum teres which supplies the head of the femur with blood. He was able to play baseball, but not like before.
The following is just my opinion, it cannot take the place of an evaluation by a medical professional who can actually see and touch your shoulder.
The problem with replacing a shoulder or a hip is that the more mobile a joint is, the less stable it is. When you start opening up the joint and replacing things, it is a challenge to get stable range of motion back.
With the shoulder replacement, I would get several opinions and ask questions about the surgical approach and if the musculature of the shoulder will be left intact. Are they going to replace the head of the humerus and the glenoid? Or just the head of the humerus? If the shoulder musculature is left intact and you religiously rehab the shoulder then you should be ok. It won't ever be like it was, but a 40# limit it pretty cautious.
If one or more of the the rotator cuff muscles are not left intact then you will have problems. Ask about trying therapy first. If it was a member of my family, I would try as many conservative measures as I could before going under the knife.
In my experience Muscle Activation Techniques would be worth a try. I find it works the best to improve stability and reduce pain whether the cause is arthritis or not. Arthritis generally comes from abnormal joint mechanics over years. MAT helps to normalize joint mechanics and stabilize joints. I have also been trained to use myofascial release. Myofascial release (or any release techniques) can go a long way to improve range of motion and pain, but very often that range is not as stable as it should be. MAT can improve your range of motion and the stability within that improved range.
For example, I have a patient right now whose orthopedic surgeon recommended a shoulder replacement and she is functioning fine. Her pain free range of motion has improved significanlty, but more importantly, her stability is good. I also had a patient who had severe arthritis of the thumbs, touching the thumb to the pinky was impossible due to pain. She had been this way for five years and was at the end of her rope. Her ortho recommended removing the trapezium bone on both sides.
He was then going to take a tendon graft from each forearm and loop it from the thumb to the index finger to create stability in the new joint surfaces. YIKES! She opted to see me instead. After six treatment sessions she was able to return to gardening, riding a bike, writing, etc without pain or instability. If you want more info., you can send me an email or PM. Hope this helps.