Personally, I probably would avoid putting anything on the boot lid unless you have a spare boot lid!
The problem with composities is that it's really hard to determine when damage has been done, any strain which is disproportionate the to the direction of the weave risks cracking or delamination; neither which is good...
Holes definitely very bad, but straps also unless they are precisely distributed risk strain being placed unevenly over the surface of the structure, excess strain on one side vs. too little on the other, and either a) the rack moves, or b) the lid moves, again undesirable.
I think that loading like is ultimately not for the Roadster, if you do try it then start with lots of padding, or maybe even better a soft bag which you strap to the lid directly, the metal rack adds mass and strain, a soft bag will mitigate some of that. My two cents of course.