Enter and replace partial value in two cells

Hello,
I 'd like to replace partial values in one cell (A5), after the value entered in the A1. For example,
In A1, I entered New York City. I have a sentence in A5 wirtten as I live in [New York City]. The New York City is in [ ]. Now I changed my value in A1 to Boston to replace New York City, the same value should replace the A5 to I live in [Boston]. Please teach me do the same on the same worksheet and as well as from one worksheet to a different worksheet.

Thanks,

Chuck