Unfortunately you cannot.
But one solution might be to use the file in a program source, than generate a compile listing and copy the specs from the listing into a new DDS scource.
There is a system API that will generate SQL/DDL source for a file object, and put it into a source file and member of your choice.
The name of the API is QSQGNDDL. This can be done through iSeries Navigator as well. Also, if you have Aldon CMS/LMi, there’s a menu option to accomplish.
Why not take this opportunity to convert your original DDS sourced object into an SQL table? The compiled SQL object will be implemented as a physical file with the same functionality as the original one compiled from DDS, and using SQL/DDL gives you more flexibility since you can utilize more of the database functionality in the future.