If yours is vintage looking, I doubt anybody would look at it and see a "fake". The only time I think something is fake is if I see added bling that doesn't belong or bright vachetta. If you make the tabs discreet and the warranty issue doesn't bother you, go for it. I for one can't wait to see it and you might start a new thing. I took a bag to the local cobbler to fix a strap and they sewed it with thread to match. I have made subtle changes to my bags by clipping longer straps on and no one has ever looked at it funny.
I have tried to clip straps to the speedy and it hangs weird.The tabs are a good idea.
I'm still thinking about it if i can find the right tabs i'll go ahead with it , i hate the way it hangs when you clip straps to it too , the cobbler i use has already fixed the strap on my messenger and he did a fantastic job you wouldn't even know it was repaired i just not sure what kind of tabs to use .