Well, I was wondering if this can be done.

If I mounted my Aimpoint on a Larue QD Cantilever mount and a magnified scope on Larue's SPR mount, could I switch them out fast?

For example, Aimpoint on when CQB but once I need to hit targets FAR out, I could quickly dismount the Aimpoint and attatch on the magnified optics within a few seconds, right? After the "far" targets have been engaged, I could pop off the magnified scope and pop on the Aimpoint and continue throughout the day.

I know it's not practical, but both hold zero even after dismounted, right?

That's an ideal setup...you could go back and forth between the two in very short order with LaRue mounts.  

I have some ARMS throwlever mounts that accomplish the same thing, but the LaRues are the best solution for this problem...IF you can afford them!  

Yeah, each mount together costs more than my magnified scope! (Burris Fullfield II)