So I know that we can use URL schemes to OPEN an app from an app, but that's not my objective.
Say I want to make an Iphone app which users can download and click a button which will launch another app ( eg.gmail for this case) and run some sort of front-end actions. For example, make the icons bigger, change colors, change the UI, highlight stuff, add pop-up text, etc. Just to re-terate, I'm not trying to modify any code on the gmail app it self. I want to code my app to do certain actions that can be "applied" or "faked" in the view of the other app.
I was thinking there could be a virtual button ideally (like the virtual assist on the iphone) that would popup on the gmail app. I'm not trying to change any functionalities or gmail's code, just want to to be able to modify the front-end experience.
Chrome extensions are easy to use in this case since you can open any site and change anything once user launches extension on the page, but is there something similar to IOS?