I've commuted an indulgence for others [conditionally, in Purgatory], and the priest said that was commuting. But commuting a penance ...might that mean doing penance for someone who can't do it? (Or would a priest
give you that look for suggesting such a thing?)
I can think of at least one I'd have rather not done

Even after I did it, I wondered about it. But I guess it brought fruits. Later. The hard way.