Paul

You may choose a colourful style for the custom coupon message, or wrap the message in your own CSS class container.
It’s also possible to hide the default message from Woocommerce so that only your custom coupon message is displayed. 
(the plugin uses inline CSS to hide the default Woocommerce message).
Take a look at the screenshots for the coupon edit screen with the plugin enabled and some examples.
The meta box was implemented using the technique described on this blog post: 
http://wp.smashingmagazine.com/2011/10/04/create-custom-post-meta-boxes-wordpress/
The message styles were generated using this tool: 
http://www.bestcssbuttongenerator.com/

Woocommerce Custom Coupon Message

This plugin adds a meta box to the coupon edit screen where you can make your own customized coupon message.

neblabs

A 100% free plugin. Free forever. No “pro” version. Premium quality. Made for WooCommerce.
Compatible with WooCommerce 9.* (latest)
Coupon URLs is a WooCommerce extension that allows you to apply a WooCommerce coupon by clicking a custom link on your site. You have full control over the URL. You can create any URL you want from your own domain, there are no limits or restrictions:
<ul>
<li>Examples:
<ul>
<li>https://example.com/?code=FALL50</li>
<li>https://example.com/code/FALL50</li>
<li>https://example.com/FALL50</li>
<li>https://example.com/offers/?code=FALL50</li>
<li>https://example.com/a/very/deep/path</li>
</ul>
</li>
</ul>
You can also add a WooCommerce product automatically before adding the coupon.
<h3>Add a product before adding the coupon</h3>
Coupon URLs allows you to add a product from your store automatically before applying the discount/coupon. You can even select the quantity!
For example, you can create a custom link like: https://example.com/code/FREEORANGE that when clicked will add 1 Orange and then the coupon FREEORANGE will be applied adding a 100% discount (just as an example).
<h3>Redirect to the cart, the checkout page or any other page after applying the coupon</h3>
You can select any page on your site to redirect to after applying the coupon. Want to redirect to the cart? The checkout page? A specific product page? A custom page? We got you covered!
Redirect to: 
* Cart (WooCommerce) 
* Checkout (WooCommerce) 
* Shop (WooCommerce) 
* Homepage 
* Any page on your site 
* A custom path on your site (eg: example.com/a/custom-path) 
* An external URL
<h3>Smart apply</h3>
If the customer’s cart is empty (and you haven’t added the Add Product action), Coupon URLs will remember to add the coupon as soon as the customer adds a product to their cart. No manual action needed.
<h3>Beautiful builder</h3>
Coupon URLs has been designed as a builder so that you can add only the actions that you want to perform after the link has been clicked, visually.
<ul>
<li>5 actions:
<ul>
<li>Add coupon.</li>
<li>Add Product.</li>
<li>Add an Extra Message After Applying to the Cart.</li>
<li>Add Custom Message When Coupon hasn’t been added yet.</li>
<li>Redirect</li>
</ul>
</li>
</ul>
Coupon URLs is an original Neblabs design. We love your opinion. If you have feedback or new ideas that you’d like to see, <a href="https://wordpress.org/support/plugin/coupon-urls-for-woocommerce/" rel="ugc">let us know</a>. You can view the repo <a href="https://github.com/Neblabs/coupon-urls" rel="nofollow ugc">here</a>.

Coupon URLs – Apply a Coupon from a Custom Link – for WooCommerce

Create coupons URLs from any URL on your site. Apply a coupon by visiting a custom link from your domain, like example.com/code/9785895

Woocommerce Custom Coupon Message vs Coupon URLs – Apply a Coupon from a Custom Link – for WooCommerce