You can use DITA2Go to convert the files in your document to ASCII DCL, specifying -t dcl on the command line (see §45.3 DCL command-line syntax). Next time you run the same conversion, you can direct DITA2Go to use those DCL files (and your altered or replaced graphics files) instead of creating them anew:
[Setup]
; UseExistingDCL = No (default, make .dcb)
; or Yes (use .dcl file if it exists)
UseExistingDCL = Yes
When you specify UseExistingDCL=Yes, instead of creating binary DCL files (extension .dcb) and then deleting them at the end of the conversion process, DITA2Go uses the existing ASCII DCL files (extension .dcl), and leaves them in place.
When you are finished with a set of DCL files, to clear them out before you begin a new conversion from your document:
[Setup]
; DeleteExistingDCL = No (default) or Yes (delete *.dcl from the
; project directory before conversion if UseExistingDCL is not set.
DeleteExistingDCL = Yes
When DeleteExistingDCL=Yes, DITA2Go deletes both .dcl and .dcb files from your project directory before conversion.