Simply explained as「person arrayed inside spread legs with raised rod and crotch」will likely be a scenario that will INITIATE ACTIONS of one sort or another. Modern replacement (更) uses「horizontal motion, array」and「taut, erection within plugged orifice」as it grows later and later into the night, with more and more renewed activity.
　「Immovable, person inside spread legs」with「forcing rod raised in crotch」as a CHANGE, ALTERED for the remainder of one's life by removing a natural blockage, such as the hymen.
　「Immobilized person, horizontal motion inside spread legs, forcing a prepubescent girl's crotch」that suggests she may have been bound to a heavy cauldron and surrounded by a gang of group members, for example, an experience that would surely CHANGE, ALTER her forever.
　Or,「immobilized person, horizontal motion inside spread legs, forcing a raised rod in crotch」by removing an unwanted blockage with a bougie: scarring from sexually transmitted diseases can cause both a shortened penis and a bent or curled penis, especially when attempting to become erect. Gonorrhea and other such diseases cause scar tissue to form within the urethra:
　「Peyronie's Disease, …also known as 'Induratio penis plastica,' or more recently 'Chronic Inflammation of the Tunica Albuginea (CITA),' is a connective tissue disorder involving the growth of fibrous plaques in the soft tissue of the penis affecting up to 10% of men. Specifically, scar tissue forms in the tunica albuginea, the thick sheath of tissue surrounding the corpora cavernosa causing pain, abnormal curvature, erectile dysfunction, indentation, loss of girth and shortening. …The disease may cause pain. Hardened, big, cord-like lesions (scar tissue known as 'plaques'). Or abnormal curvature of the penis when erect due to chronic inflammation of the tunica albuginea (CITA). Although the popular conception of Peyronie's Disease is that it always involves curvature of the penis, the scar tissue sometimes causes divots or indentations rather than curvature. The condition may also make sexual intercourse painful and/or difficult…」
　　[　https://en.wikipedia.org/wiki/Peyronie%27s_disease 2012-08-15　]　

Modern definitions (that generally disregard history) …excluding politically incorrect concepts and other meanings deemed offensive today; may list only pigeonholed definitions, euphemisms, or meaningless mnemonics)
Unihan extended: (same as 更) to change, to alter