Changing Marking Methods

Question: Is there a rule that disallows a player to mark his lie with a mini and subsequently decide to replace the disc and pick up the mini? For example, if a player throws near a bush or tree, puts down his mini, obtains his stance, and decides a few inches clearance would better facilitate the throw, replaces the disc and pick up the mini.

Response: Applicable Rules: 803.03 Marking the Lie
Yes, there is a rule that prevents replacing a picked up disc and using it as the mark after having removed it.

803.03 Marking the Lie Section A: A player may instead choose, without touching or repositioning the thrown disc, to use the thrown disc as the marker. In your example the thrower has already "touched and repositioned" the thrown disc, so it can no longer be used as the mark.

What you can do to avoid this situation is to place your mini and then go about taking your stance without touching or moving the thrown disc. Then if you decide that you'd like to play from behind the disc instead of from the mini, you can just pick up your mini.