Control Cache Expiration For Custom File On Server - apache

Question

We have files that we serve to a Native Windows OS applications from our server. The files can change every minute so we need to ensure the user is downloading the latest file.
We've found that users on Portable WiFi's tend to get served an older file. So we are changing our servers .htaccess file expirations for certain files.
We serve a custom file type (.ebc) and the files contents are sent over HTTP as plain text. In this case should we use ExpiresByType text/ebc "access 1 minute"?
Will changing .htaccess cache control affect Portable Wifi caching or will this only affect browsers?
Should mod_expires / mode_headers occur code occur before redirects and rewrites? I've discovered before that you should perform certain .htaccess code operations before others (such as place redirects at the top of the file).
Heres my code:
RedirectMatch (?i)^/wp-content/uploads/2014/10/a.exe http://www.website.com/wp-content/uploads/2014/10/b.exe
## EXPIRES CACHING Should we place this before mode_rewrite or after? ##
<IfModule mod_expires.c>
ExpiresActive On
ExpiresByType text/ebc "access 1 minute"
</IfModule>
## EXPIRES CACHING ##
# BEGIN WordPress
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteRule ^index\.php$ - [L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
# END WordPress

Answer 1

There are 3 questions here, so I'll attempt to answer them.
We serve a custom file type (.ebc) and the files contents are sent over HTTP as plain text. In this case should we use ExpiresByType text/ebc access 1 minute
That should be fine, as long as you have the text/ebc mime-type properly set on your server.
Will changing .htaccess cache control affect Portable Wifi caching or will this only affect browsers
I don't really know what "Portable Wifi caching" is. These headers are targeted at browsers only. If a custom application is downloading these files, it could be implementing its own caching and so these headers might get ignored.
Should mod_expires / mod_headers code occur before redirects and rewrites?
I'd put it before the redirects but only from a logical point of view. These are not like RewriteRules and think they get evaluated separately.
Additionally, I'll add that caching is difficult and once a file has left your server it can be hard to force an update. Different browsers behave different ways and I've come across configurations that work one place and not another.
I would additionally consider two other approaches to what you're attempting.
Firstly, don't cache your files at all:
<FilesMatch "\.ebc$">
Header set Cache-Control no-cache
Header set pragma no-cache
</FilesMatch>
Secondly think about implementing a cache-busting mechanism. If the file is linked from somewhere, try and make sure that link is changed (normally a querystring with a timestamp suffices) each time the file changes. You obviously then need to make sure whatever contains the link also isn't being cached.

Answer 2

An easier solution I used in the past was adding a parameter to the downloadable files.
For example, if the file you're serving is
http://www.domain.tld/file.pdf
then you can create the following link:
http://www.domain.tld/file.pdf?d486dFyg
The question mark and whatever comes after it (random) will be ignored but it will guarantee that the user will always download the latest version, as the URL will be different (because of the random always being different of course).
The downloaded file on the user's computer will just be file.pdf so absolutely no downside.
EDIT: I noticed some reference to WordPress in your question, which is PHP, so you can use the rand() function to append the random part: http://php.net/manual/en/function.rand.php