A Few years back we have created fmt format through PDFTEX. Now we have need to update some points in the class file. It is possible again to create fmt to .cls or .dtx files?
I believe it is possible to extract the information from format files into a form that can be turned into a TeX script, but this is likely to be a lot of work for you to turn into something you can use as a class file.
The issue is that format files characterise the initial state of the engine when it is given a document - there is no good semantics for combining two formats, (for you, your format and the Latex format), and quite possibly unresolvable conflicts. Furthermore, the contents as you get them automatically will be the contents as they are represented internally by TeX, and so will not be particularly easy to understand (think of macros defining macros,
You can extract much of the most important content of a format file using the following steps (which can be automated, but I know of no script that does so):
It would be easier to work with the sources you used to prepare the format.