I've researched the destruction and export of USGI M14 rifles. I cannot find a Presidential Executive Order that discusses "demilitarization" of DOD small arms. It may exist but as far as I can figure out, it was a decision made at the Secretary of Defense or Secretary of Army level (in 1993?). FWIW
Yes, over 450,000 USGI M14 rifles have been transferred to more than two dozen countries beginning in 1973 and continuing until at least 1998. The destruction began as early as 1970 by destroying 250 Army ROTC unit M14 rifles at Loyola University (IL). In 1993 and 1994, over 497,000 + M14 rifles were destroyed alone. IIRC, according to Scott Duff (and he does his homework), about 750,000 M14 rifles had been destroyed by the time he published his book on the M14 in 1996. Coincidentally, that's when the destruction stopped. I discuss this topic in my book M14 Rifle History and Development.
IMHO, this matter of destroying and exporting USGI M14 rifles makes civlian production of M14 type rifles all the more important.