With my Emacs 26.1 on my 10.13.6 Mac, I want Emacs to systemically open my file located at /Users/ewandelanoy/Documents/html_files/Printable/latinized_agreda2.txt with the mac-roman-mac encoding, without changing Emacs' normal behavior on other files.

Following the advice given in this answer, I added the line (modify-coding-system-alist "/Users/ewandelanoy/Documents/html_files/Printable/latinized_agreda2.txt" 'mac-roman-mac) to my init.el file, but it seems that this is incorrect since when I restart emacs I get the following (somewhat unclear) error message :

Warning (initialization): An error occurred while loading ‘/Users/ewandelanoy/.emacs.d/init.el’:

Wrong number of arguments: #[(target-type regexp coding-system) \306>\204�\307\310"\210  ;\204 �\311=\203� \250\204 �\307\312  "\210
9\2036�\313
!\204@�\314
!\210
\211B\202@�\314
@!\210\314
A!\210\315\267\202v�\316   "\211\203U�
\241\202\�  
BB\211)\207\316   
"\211\203m�
\241\202t�  
B
B\211)\207\316 "\211\203\206�
\241\202\217�   
BB\211)\207 [target-type regexp coding-system file-coding-system-alist slot process-coding-system-alist (file process network) error Invalid target type: %s network Invalid regular expression: %s fboundp check-coding-system #s(hash-table size 2 test eq rehash-size 1.5 rehash-threshold 0.8125 purecopy t data (file 70 process 94)) assoc network-coding-system-alist] 4 2267173], 2

To ensure normal operation, you should investigate and remove the
cause of the error in your initialization file.  Start Emacs with
the ‘--debug-init’ option to view a complete error backtrace.

When I start Emacs with the --debug-init option as advised, I get the following error message :

Debugger entered--Lisp error: (void-function global-linum-mode)
  (global-linum-mode t)
  eval-buffer(#<buffer  *load*<2>> nil "/Users/ewandelanoy/Documents/Bash_scripts/init.el" nil t)  ; Reading at buffer posit$
  load-with-code-conversion("/Users/ewandelanoy/Documents/Bash_scripts/init.el" "/Users/ewandelanoy/Documents/Bash_scripts/i$
  load("~/Documents/Bash_scripts/init.el")
  eval-buffer(#<buffer  *load*> nil "/Users/ewandelanoy/.emacs.d/init.el" nil t)  ; Reading at buffer position 42
  load-with-code-conversion("/Users/ewandelanoy/.emacs.d/init.el" "/Users/ewandelanoy/.emacs.d/init.el" t t)
  load("/Users/ewandelanoy/.emacs.d/init" t t)
  #[nil "^H\205\276^@   \306=\203^Q^@\307^H\310Q\202A^@ \311=\2033^@\312\307\313\314#\203#^@\315\202A^@\312\307\313\316#\203$
  command-line()
  normal-top-level()

The second error message is not really any clearer than the first. What did I do wrong ?