From Google AI.
In most cases, NFL teams can initiate a simple contract restructure, converting salary to a signing bonus, without the player's explicit agreement, as the player doesn't typically lose any money, but may need a player's consent for renegotiation or "maximum restructures".
Here's a more detailed explanation:
Unilateral Restructures:
Teams often have the ability to unilaterally execute simple restructures, which involve converting part of a player's base salary to a signing bonus.
Player Consent:
While teams can execute simple restructures without asking the player, a maximum restructure typically involves a renegotiation of the contract and requires the player's consent.
Why Players Typically Agree:
Restructures usually don't result in a player earning less money; they're an accounting maneuver that helps the team manage its salary cap by spreading payments over the remaining contract years.