How do I make the Google Chrome flag "--allow-file-access-from-files" permanent?

Navigate to the desktop launcher / menu entry, open the launcher properties dialog for google chrome.

It should look like this:

/usr/bin/google-chrome %U

To make the flags that you want permanent, modify it to something like:

/usr/bin/google-chrome --allow-file-access-from-files

You may also need to delete and re-pin your icon launchers after modifying it. Chrome should launch with the specified flags enabled after the modification.

Alternatively, you can simply create a new launcher with the above and use it to start chrome.

To check if the flags that you modified are being loaded:

$ cat ~/.config/google-chrome/Local\ State

and scroll up to the block entitled

"session_restore"

Your flags should be listed in the block, before

--flag-switches-begin --flag-switches-end.

Opening chrome and navigating to the URL

chrome://version/

should also list enabled flags in the

Command Line 

block

This is a list of the google-chrome / chromium flags:

http://peter.sh/experiments/chromium-command-line-switches/

The different modes like --allow-file-access-from-files are flags/switches and not meant for general users. So you can't change it permanently with regular builds. The purpose of these switches/argument is to provide choice. These flags are neither supported nor recommended and must be used as temporary.

Since you don't want to use .desktop file or changing any shortcut. The only thing you can do is to look into code of open source chorimium .

Customize the code and build it. Then only it will open with your desired mode.

_{List of switches | Source}