“The idea of changing it now to the Comcast Building,” said Carol H. Krinsky, a New York University art history professor and the author of “Rockefeller Center,” “strikes me the same way that the change to the G.E. Building name did: ‘I’m the new guy on the block and you are nothing anymore.’ ”

As proposed, more modest 12-foot-high light-emitting diode signs that spell Comcast in white uppercase letters would be installed on the broader north and south limestone exteriors, crowned by 10-foot-high NBC peacock logos. A 17-foot-high peacock would appear by itself on the western facade more or less facing Philadelphia. Measured in overall square feet, the new signs would be slightly more compact than the existing G.E. signs.

A new entrance and marquee would also be installed on Avenue of the Americas to promote “The Tonight Show Starring Jimmy Fallon.” (Among the other shows produced there is “Saturday Night Live,” one of whose alumni, Senator Al Franken, a Minnesota Democrat, opposes Comcast’s acquisition of Time Warner Cable.)

“Nothing has been finalized yet,” Cameron Blanchard, a spokeswoman for NBCUniversal, said of the proposed renovations.