RT5 REST2 API port to RT4

While tinkering with a test installation of RT5 I’ve noticed that RT5 REST2 API finally supports adding and removing links. Is it possible to somehow manually backport this functionality to RT4 REST2 plugin? Unfortunately we can’t move to RT5 from RT4 (got lots of custom functions written by devs who no longer work with us, these functions do not work on RT5 for some reason or another), but linking tickets and assets via API is what I’ve been craving this entire time.
Any help would be appreciated.