Search For A Hex Byte In A File?

I had made an app that opens a file and changes a hex byte then when I click another button it saves it.I am now thinking of making an app that will change some hex bytes to something else, but the catch is that not every file will have some of the hex bytes that others will. Like I want it to search for 71, 13, 31, and 11, and change them to 15, but not all files will have say a 71 or some might not have a 13 or a 31...Also, if there was a couple of bytes in a row that I needed to change, say F132, would I be able to search for all of that at once, and then change it to something like F133?