In short, yes: CFR 1910.179 governs modifications, operational and load testing for gantry cranes.
Regulation
OSHA CFR 1910.179 Overhead and Gantry Cranes outlines how to manage a crane modification in section (b)(3):
"Modifications. Cranes may be modified and rerated provided such modifications and the supporting structure are checked thoroughly for the new rated load by a qualified engineer or the equipment manufacturer. The crane shall be tested in accordance with paragraph (k)(2) of this section. New rated load shall be displayed in accordance with subparagraph (5) of this paragraph."
Section (k)(1) outlines the operational tests required when a crane has been altered, including hoisting and traveling the crane.
Lastly, section (k)(2) defines a rated load test for a new or modified gantry crane.
Standard
The modification, rating, and testing provisions from OSHA are mirrored in ASME B30.2-1.4.3 Modifications and 2-2.3 Tests section.
ASME removes any ambiguity and expands the term 'modified' to include "new, reinstalled, altered, repaired".
ITI Best Practice
Generally, when a modification is made to equipment, both an operational and load test are required to insure all components are present and in good working order.
If a modification also changes the rated load (as defined by a qualified person or manufacturer's requirement), a load test is required at the load test weight based on the new rated load.