I tried what you suggest, but it doesnt work as before:

ServiceName is username within /etc/passwd catched using ExternalList on the node.

Does not work:

if ($node->isAgent && $node->platformName like "Linux-*") {
    users = $node->readAgentList("UserList");
    if ( users == null ) return null;
    foreach ( user : users ) {
      if ( user == ServiceName ) return true;
    }
  }
  return false;

Does work, but is not the correct way..

if ($node->isAgent && $node->platformName like "Linux-*") {
    users = AgentReadList($node,"UserList");
    if ( users == null ) return null;
    foreach ( user : users ) {
      if ( user == ServiceName ) return true;
    }
  }
  return false;

However, if i add node to template first and then do "Configuration Poll" with $node->readAgentList version, it does not remove the node from template even if "Remove this template automatically when node no longer passes through filter"
It does get removed/unbind if i only put "return false;" in the Automatic Apply Rules.

readAgentList is a node object method, so if you were calling

AgentReadList($node, ...

(read agent parameter from node pointed by $node variable) you now should use

$node->readAgentList(...

to read list from agent on same node.

Best regards,
Victor