Importing play store emoticons into stock message app

[AC Question]

I have the Galaxy S5 and want to import emoticons downloaded from the play store into the stock message app. The only way I've found so far is to send the message through the downloaded app instead of message app, which means you can't add emoticon to existing app or do the whole message in a single application. Great fun emoticons in the Google store but not as fun if I can't somehow import them into the stock message app. Anyone?