Could you show an example of what you're trying to do, upload the game to somewhere as an exported HTML to show it if you don't want to share the CAPX.
Assuming you're already using an invisible box as the actual platform behvior object, you can swap it dynamically at runtime quite easily.
An abandoned project I made a while back did this.
Press down to change the ball from platform mode to physics mode.
The only difficulty I encountered was having to duplicate all the blocks to set physics behavior on one, and solid on the others.