Hi, Jody —
There was a ruling by Rome that Rachel may help to address your question.
In 1984, the Congregation for Worship and the Discipline of Sacraments Issued a ruling [Prot. No. 1031/84, October 20, 1984] stating,
“If a sponsor dies or the parents are angry with the sponsor, the parents may request that the names of substitute godparents be added to the baptismal records. It is evident that it is impossible to replace a sponsor, who was physically present at the time of baptism for the presentation of the candidate or was present through a proxy. However, another person can be named to fulfill the duties of the sponsor. This may be done by the diocesan bishop, if he judges it opportune.”
Others have interpreted based on this that:
“It seems reasonable that this could also be done by the pastor. However, the names of the sponsors at the baptism must not be removed from the baptismal register.”
I would argue, based on this reference that they might actually be able to do what they asked; namely, add to the record for the peace of their family.