db upgrade should convert tables to utf8.
for mysql simple shellscript can be used :

MYSQL="$(which mysql)"
MYSQLPARAMS="$@"
for i in $(echo "show tables;" | $MYSQL -N $MYSQLPARAMS); do
echo "ALTER TABLE $i CONVERT TO CHARACTER SET utf8 COLLATE utf8_general_ci;" | $MYSQL $MYSQLPARAMS
done

in this example general collation is used.

maybe db agnostic version is possible with direct sql