/lib/partman/active_partition/10change_name/do_option is in ubiquity 18.04.14.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 | #!/bin/sh
. /lib/partman/lib/base.sh
dev=$2
id=$3
cd $dev
open_dialog PARTITION_INFO $id
read_line x1 id x3 x4 x5 x6 old_name
close_dialog
[ "$id" ] || exit 1
db_set partman-partitioning/set_name "$old_name"
db_input critical partman-partitioning/set_name || true
db_go || exit 1
db_get partman-partitioning/set_name
open_dialog SET_NAME "$id" "$RET"
close_dialog
update_partition $dev $id
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