However, of course, there is a workaround. It comes down to editing the table E070, which is where the transport request headers are stored. To make a request modifiable again, change the field TRSTATUS from R (Released) to D (Modifiable). You can now edit it again in transaction SE10 or wherever you like.
Don’t know how to edit tables without a maintenance dialog? See this post to learn how to use SE16/SE16N for table maintenance.
Be warned: When modifying SAP ERP® system tables, act with caution! You should always know what you’re doing, otherwise you might cause inconsistencies and corrupted data. Also, never attempt this with a transport request that has already been moved to the subsequent system.