Sadly I don’t have the skills to implement it... I just got the idea (or need) and felt like making the suggestion to anyone with enough skills to implement it
Basically it works like this: When the Start workbench starts, a web view is automatically created, and then the StartPage.handle() function is called to produce the html code that is inserted in the webview (all happens in Start/Gui/Workbench.cpp, line78 onwards).
After this is done, the reference to the created webview is lost so there is no way to fill it with the contents of StartPage.handle() again.
If you absolutely need to reload the whole start page, then the best way is probably replace Start/Gui/Workbench.cpp line 105, instead of webView=..., make it something like FreeCADGui.webView =... So after the start WB is started, you can do something like this:
But it's less elegant and more complicated. I would try the JS way. Have a look at the StartPage.js, it has several functions that update the contents of divs to use as examples...