#!/bin/bash
s="User's name is adam
Account's name is adam_acc
User's name is adam.eve
Account's name is adam.eve_acc"
sed 's/\<adam\.eve_acc\>/user_4/g; s/\<adam_acc\>/user_3/g; s/\<adam\.eve\>/user_2/g; s/\<adam\>/user_1/g;' <<< "$s"