F#'s classes, the types from your example above, do not support copy, you would need to implement this yourself by copying all thier fields.

F#'s record types support copy and changing by the keyword "with", i.e.

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let person =
    { FirstName: string;
      LastName: string; }

let rob = { FirstName = "Robert"; LastName = "Pickering" }
let married = { rob with LastName = "Townson" }

Since equality is by structual comparison (two records with the same content are equal) there's no really need to copy records if you don't indent to make a change.

Cheers,
Rob