Bicycle Tutor

Ok I need to know if this is even possible? I noticed on other sites there are 6speed and 7 speed Adult tricycles. I was pondering the idea of modifying a Schwinn Meridian 2008 model into maybe a 6speed. Before I go any further is that even possible without getting into major work?
If so, then what about expanding that idea into a 12speed by swapping out its current crank with an older Schwinn 10speed crank? Yes I know it would need a front derailleur. Is this even worth the effort? Thanks for ANY input.