Making your Annette Himstedt doll, or actually any collectable doll for that matter, worthless is easy!  Any one of these will devalue your doll considerably.  The more you do of these steps, the less your doll will be valued by collectors:

Step 1: Restyle their wig or permanently change any aspect of the doll.

Step 2: Display your doll in a smoking environment and in direct sunlight.

Step 3: Sell, destroy or lose the original outfit (or any part of it).

Step 4: Sell, destroy or lose the Certificate of Authenticity

Step 5: Get rid of the shipper.

In short, if you want to maintain the value of your dolls you need to keep them as close to original condition as possible.  If you like to play with the dolls then at the very least be sure to not make any permanent changes to them, and be sure to keep EVERYTHING that came with them, including the shipping boxes, because yes they are important!