The procedure you are referring is 120.4 Commodity Jurisdiction. Yes you can self designate, but you had better be correct! It is easier to simply request the DDTC to provide a "CJ" in writing for the defense article in question. The DDTC takes into account the number, variety and predominance of civil applications, the nature, function and capability of the civil applications and the nature, function and capability of the military applications.
Take care and don't confuse Dual-Use vs. USML. Per 120.3 it is ITAR Controlled if: Is specifically designed, developed, configured, adapted, or modified for military application,...
If the part was originally designed for a civil application, i.e. a fastener for a commercial aircraft and then used in a military aircraft (without modification), then it is considered Dual-Use and ITAR does not apply.