Wordpress disable out-of-the-box rest-api, use library instead - json

Question

In newer Wordpress, there is REST-API in the core.
Previously used plugin (specifically WP-API-1.2.3) had different API base URL (e.g. /wp-json/posts), but the newer one is using different structure (e.g. /wp-json/wp/v2/posts).
In order to be backward compatible, I want to support older version and not changing the base of API - otherwise, all other pages using this service would no longer work.
I found how to change the "wp-json" part, but not namespace "/wp/v2/".
Is there a way around how to use the original base path and in the best case to be sure nothing will go wrong to use the older library instead of the newer core functionality?
Disabling it in functions.php can't solve this issue - it's shutting down the lib.
add_filter('json_enabled', '__return_false');
add_filter('json_jsonp_enabled', '__return_false');
Thanks

Answer 1

Basically, there were 2 things I did and it's working:
rest_url_prefix was the same like in previous version (wp-json), paths were writing over each other (after requesting something like wp-json/posts went through the new core part of WP, not the lib).
function rest_get_url_prefix() {
return apply_filters( 'rest_url_prefix', 'newPrefix' );
}
I didn't click on Settings -> Permalinks -> Save changes
By doing this I am now able to use the original endpoints