Yes, you can. But...
1) The loadbalancer will be placed in his own tab (not Deployments nor Machines) and cannot be added to an existing deployment.
2) It takes some effort (at least the first time) to develop this solution.
Here is a video I've made with vRA 6.2 but it's almost the same solution for 7.x:
(I have a new version with better looking actions)
In the youtube channel you will find same solution for DNat and Firewall rules.
Is this what you have in mind?
Yes. This is what I am looking for.
I am looking for a code to create and present loadbalancer object to the vRA GUI so that users can use custom actions to add node or reconfigure
Well, as you could see, it is possible (I've done it). But it's too complex to share it here.
My solution was to create my own custom object with Dynamic Types plugin. But I'm sure that you can use an object from the NSX plugin.
If you want something like you saw in the video then yes. But you could find a easier approach using an existing NSX object like "Pool". As I said before, I had to learn a couple of things as prerequisites of what is showed in the video.