Jerryvoc,
1st question to ask is when was the strata plan registered for the building that you are in. 2nd question to ask is whether the balcony door is yours already.
In strata plans that were registered under the original Strata Act, in the 1960’s, the balcony door wall window structure is not common property as such. In the 1973 act, it depends on how the strata plan was drawn as to whether it is or isn’t common property.
I would have to suggest that if you are looking at replacing the door you would want to make sure that the sealing of this structure is done correctly and or that you get the correct warranties from the contractors on completing the work.
If the door is common property the correct process would involve getting approval by a special resolution and exclusive use by-law.