OK. I checked and here is the applicable factors I think.
60. In what other ways can an existing contract be modified?
Other than extensions (see question number 58) and renegotiations (see question number 59), a team and player can mutually modify an existing contract as follows:
- To alter the amount of compensation protection -- i.e., the guarantee (see question number 63). This is commonly done as part of a buyout (see question number 66).
- To eliminate an option or ETO (see question number 57). Note that eliminating an option does NOT constitute illegally shortening a contract, since an option year isn't considered part of the original term of a contract until it is invoked.
- To reduce the amount of a trade bonus (see question number 99).
- To waive set-off (see question number 65), which is commonly done in conjunction with a buyout (see question number 66).
- To alter the pay schedule (see question number 115). However, when a contract signed under the current CBA is terminated through the waiver process, the pay schedule is automatically "stretched" (see question number 64).
- To alter the window of time during which an option may be invoked (rare).
- To alter the list of outside activities in which the player is allowed to participate (rare).
- To change the section of the standard contract that permits the team to suspend the player if the player does not maintain sufficient physical condition.
The last year of Anderson's contract is essentially an option year for BOTH player and team. It is a PLAYER option for an additional year at $21 million. It is a TEAM option to waive the player with a guaranteed $15.6 million. Changing the player guaranteed portion of the option can be mutually modified under bullet point 2. If an option can be eliminated, I assume it can also be altered by mutual agreement.