Wouldn't switching the hydraulic fluid be sufficient? It's not like there's one single hydraulic fluid in existence, there's thousands of natural and artificial

Wouldn't switching the hydraulic fluid be sufficient? It's not like there's one single hydraulic fluid in existence, there's thousands of natural and artificial fluids that can be used in hydraulics. The hydraulic fluid was obviously chosen for California weather not Minnesota, so the hydraulic fluid could suitably be changed for operating in lower temperature ranges.