substitution

Definition from Nolo’s Plain-English Law Dictionary

Putting one person or thing in the place of another. For example, a substitution of parties takes place when a new party is named to take the place of a party who has died or is otherwise unable to continue as a party. Or, one attorney might substitute into a case to replace the attorney of record if, for example, the client fired the first attorney.

Definition provided by Nolo’s Plain-English Law Dictionary.