Short answer: Yes it is possible to add grips to control Height/Width parameters in a family after inserting into the project
it's not clear in which context you want to use such a balustrade so I am not sure how to elaborate more with the answer. Im also not sure how such grips would function with a rail which has 100 balusters! on a nonregular/sloped/curved path!!! I would suggest that the top rail goes with grips and balusters be adaptive...
If you provide more details, handsketch or anything...maybe one can give you a screencast; otherwise, if you are not looking for something specific, there are lots of Adaptive Railing tutorial as well as turtorials on how to add grips to families. I know @Alfredo_Medina has something about Adaptive Railing on his Youtube channel you could check out HERE there are also some examples about Adaptive components and parametric families (with and without grips) on the Autodesk Knowledge Netwrok which are usefule .
