Here's a small program that I made in Python. The code was inspired from Mike Dane. (He's really good, go check him out too at MikeDane.com) My program allows the user to replace a letter to another specific one in a given sentence..
Please do upvote and check out some of my other cool stuff..
A nice thing to add would be a loop, using while True or a for loop, just so you don't have to re-run the program for each new sentence.