#2 Corbin offers to be a guest referee

Corbin should not fulfil Angle's last wish because doing so will not justify his role. Being a heel means that he can be more demanding. Giving everything that their peers want is not something that heels do.
Heels need to be callous and conniving. They also need to be a bit manipulative. During the March 18th episode of RAW, Corbin learned that he will enter WrestleMania with a loss of momentum after being defeated by Apollo Crews.
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Why would he want to be involved in a match which he suspects that he would be losing? Thus, the Lone Wolf can choose to opt out of the match but still get involved as a referee.
Corbin can get special permission from the higher-ups to be the referee. Imagine how it would be if Corbin makes a choice to be the guest referee and finds out that The Undertaker will be facing Kurt Angle.
Corbin as a referee in the match between legends like The Undertaker and Kurt Angle would mean that he gets to be involved in an iconic moment. Corbin can even give some cheap shots to the Undertaker and Kurt Angle to get some heel heat.