Infrared light carries information about heat and objects hidden by ordinary visible contrast. Giving humans this sense would change perception and technology.
What changes first
Infrared vision could reveal warm objects in darkness and make some thermal patterns visible. But infrared is not automatically equivalent to ordinary vision: the eye and brain would need a mechanism for detecting and interpreting longer wavelengths.
The physical or biological constraint
Established science
The scenario should be treated as a thought experiment. Where the consequences depend on unknown parameters, there is no single precise outcome.