Recently, I have noticed Google changed the search layout on mobiles. One example is that the links are now smaller than before. Is it possible to revert to the old style? Finding this a bit jarring.
Generally, what happens is that Google does A/B testing (where some users get a new design while the rest get the old). If they decide to update the design as a result of that testing, the old design will be replaced entirely. For the changes you're talking about, there's no going back to the old design, especially not with the limited customization available nearly across the board with mobile browsers (for example, no userscript support). The only alternate design that exists is the desktop version of the site, which is overall harder to use on mobile (though you can switch to it if your browser allows you to "request desktop site").
However, with text size, either your device or your mobile browser will allow you to change that. Here's Google Chrome iOS with normal text (top) and bigger text (bottom), applied using the "zoom text" feature:
Because I made this change in the browser itself, it only affects Google.com, not other sites or apps.
Unfortunately no. This change is irreversible by standard means.
Further complains can be sent to: https://www.google.com/tools/feedback/