Distinguish file types by extension instead than mime

[Booting1852]

I posted the same topic on Mint Forum but no one answered, may be that here is more indicated.
Because often same mime type is used from different applications (like XML format for example, or plain text) I had to continuously reassign default application to files with different extension but the same mime type.
Yes editing mime type is possible; but it is very boring respect to simply act Open With from file browser.

So I modified nemo-file-utilities.c as follows:
[code]
gchar *
nemo_get_best_guess_file_mimetype (const gchar *filename,
GFileInfo *info,
goffset size)
{

g_return_val_if_fail (filename != NULL, g_strdup ("application/octet-stream"));
g_return_val_if_fail (info != NULL, g_strdup ("application/octet-stream"));

gchar *mime_type = NULL;

if (size > 0) {
    /* Default behavior */
    mime_type = g_strdup (g_file_info_get_attribute_string (info, G_FILE_ATTRIBUTE_STANDARD_CONTENT_TYPE));

    if (mime_type == NULL) {
        mime_type = g_strdup (g_file_info_get_attribute_string (info, G_FILE_ATTRIBUTE_STANDARD_FAST_CONTENT_TYPE));
    }
} else {
    gboolean uncertain;
    gchar *guessed_type = NULL;

    /* Only give the file basename, not the full path.  a) We may not have it yet, and
     * b) we don't want g_content_type_guess to keep going and snoop the file.  This will
     * keep the guess based entirely on the extension, if there is one.
     */
    guessed_type = g_content_type_guess (filename, NULL, 0, &uncertain);

    /* Uncertain means, it's not a registered extension, so we fall back to our (gio's)
     * normal behavior - text/plain (currently at least.) */
    if (!uncertain) {
        mime_type = guessed_type;
    } else {
        mime_type = g_strdup (g_file_info_get_attribute_string (info, G_FILE_ATTRIBUTE_STANDARD_CONTENT_TYPE));
        g_free (guessed_type);
    }
}
			//Part modified by me//*****************************
if ((g_strrstr(mime_type,"text/")==mime_type)||(g_strrstr(mime_type,"xml")!=0)||(g_strrstr(mime_type,"application/zip")==mime_type)||(g_strrstr(mime_type,"octet-stream)")!=0)){
	gchar *dot = g_strrstr(filename, ".");	
	if (!(!dot || dot == filename)){mime_type = g_strdup (dot+1);}
}
return mime_type;

}
[/code]
And nemo-mime-actions.c as follows:
[code]
[...]
char* toLower(char* s) { //Parte aggiunta
for(char *p=s; *p; p++) *p=tolower(*p);
return s;
}

GAppInfo *
nemo_mime_get_default_application_for_file (NemoFile *file)
{
GAppInfo *app = NULL;
char *mime_type;
char *uri_scheme;

if (!nemo_mime_actions_check_if_required_attributes_ready (file)) {
    if (file_has_local_path (file)) {
        return NULL;
    }
}

uri_scheme = nemo_file_get_uri_scheme (file);

if (!g_str_has_prefix (uri_scheme, "http")) {
    mime_type = toLower(nemo_file_get_mime_type (file));	//Modificata
    app = g_app_info_get_default_for_type (mime_type, !file_has_local_path (file));

[...]
[/code]

On Nemo 5.8.4 it works well but I have a question:

Where I could act to make so that icon of files is the same of the associated application ? At the moment showed icons are still based on mime type.

Which are files and functions involved ?

Thank you