Yes!
But, only if they are turtles (programmable objects). Yes, you can stamp an image on top of another stamped image, but you cannot then change their order afterward—because it has become a painting!
If you have more than one turtle on the page, you can move them infront or inback of one another.
For this, you will need to know how to talk to a particular turtle so that the correct one moves. See Talking to Specific Turtles.
To get the turtle named t1 in front of another turtle, type:
t1, infront
inback works the same way.