Yes they'll change but I'm not 100% sure that'll mean your code will fail. I'm also pretty sure you can talk an older version of ontapi to a newer controller.
Inside the sdk for java bindings there's a javadoc jar file for each version of ontap. I extracted 8.0.3 and 8.2.2 and then did a manual look at each to see. Many of them are different just in possible error codes (presumably because of cluster mode) but some have different inputs and outputs like SnapmirrorResyncRequest and it's response. Again I'm not able to tell if this is just between 7-mode and cluster mode or between ontapi versions.
I do happen to have a few older filers around so I grabbed the ontapi versions for reference, not sure if that helps at all.
ontapi 1.13 - ontap 8.0.3
ontapi 1.18 - ontap 8.0.5P1
ontapi 1.19 - ontap 8.1.4P1
In the API documentation you can find a file called SDK_help.htm which will outline what APIs have been changed. Unfortunately you need to hunt around a bit to find this documentation and the corresponding OnTap versions, although this is better after 8.2 as the doc matches the ontap version.
8.3 API Documentation (probably not as helpful)
8.2.2 API Documentation (best link I could find, about 2/3 way down)