Specifying a custom node id when creating new content I want to prevent merge conflicts caused by POST requests on the API at a later stage. Is it possible to specify a custom node id when creating new content in the Drupal user interface or database? What's the fastest, most efficient way to do this?
In the UI no, and you should never interact with the database directly.

But you can do this with the API easily:

$node = Node::create(['type' =&gt; 'article', 'nid' =&gt; 5]);
$node-&gt;enforceIsNew(TRUE);
$node-&gt;save();