UPDATE Links SET Target=REPLACE(Target, ....);
UPDATE Transactions SET NewValue=REPLACE(NewValue, ...) WHERE ObjectType='RT::Ticket' AND NewValue LIKE '% ... %';
UPDATE Transactions SET OldValue=REPLACE(OldValue, ...) WHERE ObjectType='RT::Ticket' AND OldValue LIKE '% .... %';
And now used rt-validator to check if something is incorrect. Looks like my “manual” changing of links worked fine.