If you have RTB you can edit the door limit through the servers preferences.
If you don't, just find the file "JVS_Content.cs" in Blockland/config/server and edit it.
Change:
$JVS::Content::MaxContentBricksPerPlayer = 25;
to
$JVS::Content::MaxContentBricksPerPlayer = (new door limit here);
Replacing (new door limit here) with your desired door limit, of course.