Multiple encodings in one file

[Lambert, Joshua D]

Question: If I open a file that uses one encoding in one part of the file and 
another encoding in another part of the file, and also uses multiple character 
sets, can I edit a small part of it in Emacs, using UCS (Unicode), without 
Emacs changing the rest of the file?

Background: I work in a library ( the book kind) and use MARC files 
(https://www.loc.gov/marc/). MARC is a file transmission format that may have 
multiple "records." These records may contain text encoded in ISO/IEC 10646:202 
(Unicode) or MARC-8 
(https://www.loc.gov/marc/specifications/speccharintro.html), an encoding used 
mainly/only by libraries for MARC files. Libraries may have records of both 
types and one file may have records with both encodings, and multiple character 
sets. I'm attempting to write a major mode to work with these files in Emacs. 
Emacs does not recognize the MARC-8 encoding.

Thanks for your help,

Joshua Lambert
Librarian
Missouri State University