If it is flyscreens you are referring to and your complex has adopted the model bylaws, then it does say under Item 5 damage to common property, though an owner cannot mark, paint….or otherwise damage or deface etc, in subaragraph (3) that this by law does not prevent an owner or person authorized by an owners to install (b) any screen or other device for prevent entry of animals or insects on the lot. It later states that any such devices must be installed correctly and be in keeping with the appearance of the rest of the building.
If the handrails you are referring to are handrails on the outside of the townhouses, rather than have each owner draw up their own special by law to install a handrail in their nit, why don’t you have one drawn up for the whole complex that stipulates what type, colour of handrail is permitted in the complex and where exactly they can be fitted and which company to use. Though beware that any company you authorize to do such works may not be in business when the next owner wants a handrail and another company may not produce the same handrail. Then you could well end up with a mixed bag of handrails affecting the look of the complex.
Why don’t you look into getting handrails installed for all units by the OC. Get quotes and if extra monies are required you could spread a special levy over a few quarters to ease the cost to owners. In this way you can control the look of your complex. And handrails are not only handy for the elderly, they can make it easier and safer for a lot of people.