Find and replace multiple characters

Info:
Find and replace “a” with “able”. “b” with “bob”. ect…

Problem:
I can change “a” to “able” the next line would change b, but it would change the string i just changed.

Example of what it does now:
input: able to do this?
output: aboble to do this?

Question:
Can anyone make an example would be able to do this (just the a, and b, but allow me to add the rest of the letters easily)?