Is it permissible to replace the ends on an extension cord?

Extension cords used in construction may be repaired, so long as the repair is as strong as the original condition as required by 1926.403(a).

“Each cord set, attachment cap, plug and receptacle of cord sets, and any equipment connected by cord and plug, except cord sets and receptacles which are fixed and not exposed to damage, shall be visually inspected before each day’s use for external defects, such a deformed or missing pins or insulation damage, and for indications of possible internal damage.  Equipment found damaged or defective shall not be used until repaired.”

Repairs of extension cords are therefore permitted.  However the repairs must return the equipment to the state in which it was initially approved.