Why are you trying to control this with the SolidWorks API in the first place?
The only way to activate many commands using the API is via ISldWorks::RunCommand. Please see my blog post on that topic.
You will want to search swCommands_e for keywords related to what you're doing, like "property" or "pane", etc.
... the goal is ... when i want it to, split the feature manager into two panes
show it 1 / 4, 1 / 2, 3 / 4, or else... ( that already works fine ...)
...but 90% of the time, i like the two panes to show the
feature tree on the upper 3/4, and the properties pane ( to show the constraints )
on the lower 1/4 ....
BUT, every once in a while, the lower pane keeps on resuming to show
the feature tree again ... ( showing the feature tree twice is rarely usefull .. )
i want to have full control on what each pane shows ...