Fixed port for service

If one wanted to create a fixed port from the DSDL eg. 100.rmap.module.Test.1.0 (Data type definition v1.0 with fixed port-ID 100), I read from the specification that it is allowed although not recommended. It’s correct?

Specifications to
Table 2.1 (page 5): Data type taxonomy

(Private → Fixed port identifiers)

Using ranges: → Subject-ID Service-ID Purpose
[0, 6143] [0, 255] Unregulated identifiers (both fixed and non-fixed).

Yes, it is possible, but strongly discouraged, consider this an anti-pattern. If you must, you can create one, but be sure that your definitions are not available to the public or any third parties because that would risk creating conflicting port-IDs.